Electrochemical cell

ABSTRACT

Electrochemical cells including components and configurations for electrochemical cells, such as rechargeable lithium batteries, are provided. The electrochemical cells described herein may include a combination of components arranged in certain configurations that work together to increase performance of the electrochemical cell. In some embodiments, such combinations of components and configurations described herein may minimize defects, inefficiencies, or other drawbacks that might otherwise exist inherently in prior electrochemical cells, or that might exist inherently in prior electrochemical cells using the same or similar materials as those described herein, but arranged differently.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/862,528, filed Aug. 24, 2010, which is a continuation-in-part of U.S.application Ser. No. 12/535,328, filed Aug. 4, 2009, which claimspriority to U.S. Application No. 61/086,329, filed Aug. 5, 2008; U.S.application Ser. No. 12/862,528, filed Aug. 24, 2010, is also acontinuation-in-part of U.S. application Ser. No. 12/727,862, filed Mar.19, 2010, which claims priority to U.S. Application No. 61/161,529,filed Mar. 19, 2009; U.S. application Ser. No. 12/862,528, filed Aug.24, 2010, also claims priority to U.S. Application No. 61/237,903, filedAug. 28, 2009 and U.S. Application No. 61/236,322, filed Aug. 24, 2009,which are hereby incorporated by reference in their entirety.

FIELD OF INVENTION

The present invention relates to electrochemical cells, and morespecifically, to components and configurations for electrochemical cellsincluding rechargeable lithium batteries.

SUMMARY OF THE INVENTION

Electrochemical cells, and more specifically, components andconfigurations for electrochemical cells including rechargeable lithiumbatteries are generally described. The subject matter of the presentinvention involves, in some cases, interrelated products, alternativesolutions to a particular problem, and/or a plurality of different usesof one or more systems and/or articles.

In one aspect, an electrochemical cell is described. The electrochemicalcell can comprise, in some embodiments, a first electrode comprising afirst base electrode material layer comprising a first active electrodespecies, a second base electrode material layer comprising the firstactive electrode species, at least one protective layer positionedbetween the first and second base electrode material layers, a currentcollector, and a release layer, wherein the current collector ispositioned between the release layer and the first base electrodematerial layer. In some embodiments, the electrochemical cell can alsocomprise a second electrode comprising a second active electrodespecies; a polymer gel layer positioned between the first and secondelectrodes; and an electrolyte, wherein the electrochemical cell isconstructed and arranged to apply, during at least one period of timeduring charge and/or discharge of the cell, an anisotropic force with acomponent normal to a surface of the first electrode.

The electrochemical cell can comprise, in some cases, an anodecomprising a first base electrode material layer comprising lithium asan active electrode species; a second base electrode material layercomprising lithium as an active electrode species; a first multi-layeredstructure comprising a polymer layer and a lithiated single-ionconductive layer positioned between the first and second base electrodematerial layers; a second multi-layered structure comprising a polymerlayer and a lithiated single-ion conductive layer positioned between thesecond base electrode material layer and an electrolyte; a cathodecomprising sulfur as an active electrode species; and an electrolytecomprising an N—O additive, wherein the electrochemical cell isconstructed and arranged to apply, during at least one period of timeduring charge and/or discharge of the cell, an anisotropic force with acomponent normal to a surface of the first electrode.

In some embodiments, the electrochemical cell can comprise an anodecomprising a first base electrode material layer comprising lithium asan active electrode species, a second base electrode material layercomprising lithium as an active electrode species, and at least oneprotective layer positioned between the first and second base electrodematerial layers. In some cases, the electrochemical cell can alsocomprise a cathode comprising a base electrode material layer comprisingsulfur as an active electrode species, wherein the base electrodematerial layer of the cathode comprises a sulfur loading of at least 1.2mg S/cm² and a thickness of less than or equal to about 100 microns.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control. All patents and patentapplications disclosed herein are incorporated by reference in theirentirety for all purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 is a schematic diagram of an electrochemical cell, according toone set of embodiments;

FIG. 2 is a schematic diagram of an anode including a multi-layeredprotective structure, according to one set of embodiments;

FIG. 3 is a schematic diagram of an anode including multiplemulti-layered structures, according to one set of embodiments;

FIG. 4 is a schematic diagram of an anode including multiple baseelectrode material layers and an embedded layer, according to one set ofembodiments;

FIG. 5 is a schematic diagram of an anode including multiple baseelectrode material layers and an embedded multi-layered structure,according to one set of embodiments;

FIGS. 6A and 6B are schematic diagrams showing electrode assembliesincluding a release layer, according to one set of embodiments;

FIGS. 7A and 7B are schematic diagrams showing the joining of twoelectrodes to form an electrode assembly according to one set ofembodiments; and

FIGS. 8A-8D include exemplary cross-sectional schematic illustrationsoutlining the fabrication of an electrochemical cell, according to oneset of embodiments.

DETAILED DESCRIPTION

Electrochemical cells including components and configurations forelectrochemical cells, such as rechargeable lithium batteries, areprovided. The electrochemical cells described herein may include acombination of components arranged in certain configurations that worktogether to increase performance of the electrochemical cell. In someembodiments, such combinations of components and configurationsdescribed herein may minimize defects, inefficiencies, or otherdrawbacks that might otherwise exist inherently in prior electrochemicalcells, or that might exist inherently in prior electrochemical cellsusing the same or similar materials as those described herein, butarranged differently.

There has been considerable interest in recent years in developing highenergy density batteries with lithium containing anodes. Lithium metalis particularly attractive as the anode of electrochemical cells becauseof its extremely light weight and high energy density, compared forexample to certain anodes, such as lithium intercalated carbon anodes,where the presence of non-electroactive materials increases weight andvolume of the anode, and thereby reduces the energy density of thecells, and to other electrochemical systems with, for example, nickel orcadmium electrodes. Lithium metal anodes, or those comprising mainlylithium metal, provide an opportunity to construct cells which arelighter in weight, and which have a higher energy density than cellssuch as lithium-ion, nickel metal hydride or nickel-cadmium cells. Thesefeatures are highly desirable for batteries for portable electronicdevices such as cellular phones and laptop computers where a premium ispaid for low weight. Unfortunately, the reactivity of lithium and theassociated cycle life, dendrite formation, electrolyte compatibility,fabrication and safety problems have hindered the commercialization oflithium cells.

Lithium battery systems generally include a cathode which iselectrochemically lithiated during the discharge. In this process,lithium metal is converted to lithium ion and transported throughelectrolyte to the battery's cathode where it is reduced. In alithium/sulfur battery, lithium ion forms one of a variety of lithiumsulfur compounds, at the cathode. Upon charging, the process isreversed, and lithium metal is plated, from lithium ion in theelectrolyte, at the anode. In each discharge cycle, a significant number(e.g., 15-30%) of available Li may be electrochemically dissolved in theelectrolyte, and nearly this amount can be re-plated at the anode uponcharge. Typically, slightly less lithium is re-plated at the anode ateach charge, as compared to the amount removed during each discharge; asmall fraction of the metallic Li anode typically may be lost toinsoluble electrochemically inactive species during eachcharge-discharge cycle.

This process is stressful to the anode in many ways, and can lead topremature depletion of Li and reduction of the battery cycle life.During this cycling, the Li anode surface can become roughened (whichcan increase the rate of field-driven corrosion) and Li surfaceroughening can increase proportionally to the current density. Many ofthe inactive reaction products associated with overall Li loss from theanode upon cycling can also accumulate on the increasingly roughened Lisurface and may interfere with charge transport to the underlyingmetallic Li anode. In the absence of other degradation processes inother parts of the battery, the per-cycle Li anode loss alone caneventually render the cell inactive. Accordingly, it is desirable tominimize or inhibit Li-loss reactions, minimize the Li surfaceroughness/corrosion rate, and prevent any inactive corrosion reactionproducts from interfering with charge transport across the Li anodesurface. Especially at higher current density (which is commerciallydesirable) these processes can lead to quicker cell death.

The separation of a lithium anode from the electrolyte of a rechargeablelithium battery or other electrochemical cell can be desirable for avariety of reasons, including the prevention of dendrite formationduring recharging, reaction of lithium with the electrolyte, and cyclelife. For example, reaction of a lithium anode with the electrolyte mayresult in the formation of resistive film barriers on the anode, whichcan increase the internal resistance of the battery and lower the amountof current capable of being supplied by the battery at the ratedvoltage.

While a variety of techniques and components for protection of lithiumand other alkali metal anodes are known, especially in rechargeablebatteries, these protective coatings present particular challenges.Since lithium batteries function by removal and re-plating of lithiumfrom a lithium anode in each charge/discharge cycle, lithium ion must beable to pass through any protective coating. The coating must also beable to withstand morphological changes as material is removed andre-plated at the anode.

Other challenges associated with lithium/sulfur cells also exist, someof which are described in more detail below. Despite the variousexisting approaches proposed for forming lithium anodes, interfacialand/or protective layers, electrolytes, sulfur cathodes, and othercomponents, improvements are needed. Such improvements are provided inmore detail below.

While much of the description herein is directed to lithium cells(especially lithium metal/sulfur cells), it should be understood thatembodiments described herein can be applied to other types ofelectrochemical cells as well.

Examples of electrochemical cells, components, and configurations arenow provided.

FIG. 1 shows an example of an electrochemical cell including variouscomponents according to one set of embodiments. As shown in thisexemplary embodiment, electrochemical cell 10 includes an anode 15comprising a first base electrode material layer 20 comprising anelectroactive material. The base electrode material layer may bepositioned adjacent a current collector 25. Certain anodes may include arelease layer 27 which may be useful during fabrication of the anode, asdescribed in more detail below.

In certain embodiments, the base electrode material layer may beprotected by a first multi-layered structure 30, which can include, forexample, one or more single-ion conductive layers and/or one or morepolymer layers (not shown). The multi-layered structure may, in someembodiments, act as an effective barrier to protect the electroactivematerial from reaction with certain species in the electrolyte. As shownin the illustrative embodiment of FIG. 1, anode 15 also includes asecond base electrode material layer 35 separated from the first baseelectrode material layer. This second layer of electroactive materialmay shield the first base electrode material layer from damage duringcharge and/or discharge, thereby increasing the cycle life of theelectrochemical cell. A second multi-layered structure 40 may be used toprotect second base electrode material layer 35.

Electrochemical cell 10 may further include a cathode 50 comprising abase electrode material layer 55 comprising an electroactive material.Base electrode material layer 55 may be positioned adjacent a currentcollector 60, in some embodiments via a primer layer 65 which mayfacilitate adhesion between the base electrode material layer and thecurrent collector. In certain embodiments, the cathode is constructedand arranged to be structurally stable during the application of a forceto the electrochemical cell. This application of force may enhance theperformance of the electrochemical cell, as described in more detailbelow.

An electrolyte may be positioned between the anode and the cathode. Theelectrolyte can function as a medium for the storage and transport ofions, and in the special case of solid electrolytes and gelelectrolytes, these materials may additionally function as a separatorbetween the anode and the cathode. In some embodiments, anelectrochemical cell may include a heterogeneous electrolyte comprisinga first electrolyte solvent and a second electrolyte solvent. The firstand second electrolyte solvents may be partitioned during cycling, suchthat the first electrolyte solvent resides predominately at the anodeduring the cycle life of the electrochemical cell. In some embodiments,the first electrolyte solvent resides predominately at a polymer layer75 adjacent the anode. The second electrolyte solvent may residepredominately at an optional polymer layer 80 adjacent the cathodeand/or in pores of the base electrode material layer 55 of the cathode.As described in more detail below, the use of a heterogeneouselectrolyte, and especially the partitioning of a heterogeneouselectrolyte into different portions of the cell, can reduce the level ofexposure of a component of the cell to a species that may be otherwiseharmful to that component.

The various components shown in FIG. 1 will now be described in moredetail. It should be understood that not all components shown in FIG. 1need be present in the electrochemical cells described herein.Furthermore, electrochemical cells may include additional componentsthat are not shown in FIG. 1. An electrochemical cell may also includeother configurations and arrangements of components besides those shownin FIG. 1.

FIG. 2 shows one example of an anode including a multi-layered anodestabilization structure that may be included in electrochemical cellsdescribed herein, such as the electrochemical cell shown in FIG. 1(e.g., anode 15 of FIG. 1 may be in the form of anode 110 shown in FIG.2). In the embodiment illustrated in FIG. 2, anode 110 includes a baseelectrode material layer 120 (e.g., comprising an electroactive materialsuch as lithium) and a multi-layered structure 122. In some casesherein, the anode is referred to as an “anode based material,” “anodeactive material,’ or the like, and the anode along with any protectivestructures are referred to collectively as the “anode.” All suchdescriptions are to be understood to form part of the invention. In thisparticular embodiment, multi-layered structure 122 includes a single-ionconductive material 150, a polymeric layer 140 positioned between thebase electrode material and the single-ion-conductive material, and aseparation layer 130 (e.g., a layer resulting from plasma treatment ofthe electrode) positioned between the electrode and the polymeric layer.Multi-layered structures can allow passage of lithium ions and mayimpede the passage of other components that may otherwise damage theanode. Advantageously, multi-layered structures can reduce the number ofdefects and thereby force a substantial amount of the surface of thebase electrode material to participate in current conduction, impedehigh current density-induced surface damage, and/or act as an effectivebarrier to protect the anode from certain species (e.g., electrolyteand/or polysulfides), as discussed in greater detail below.

Anode 120 can comprise a base electrode material such as lithium metal,which can serve as the anode active material. The lithium metal may bein the form of, e.g., a lithium metal foil or a thin lithium film thathas been deposited on a substrate, as described below. The lithium metalmay also be in the form of a lithium alloy such as, for example, alithium-tin alloy or a lithium aluminum alloy.

In most embodiments described herein, lithium rechargeableelectrochemical cells (including lithium anodes) are described; however,it is to be understood that any analogous alkali metal battery (alkalimetal anode) can be used. Furthermore, in some embodiments, non-lithiumbased anodes can be used. Additionally, although rechargeableelectrochemical cells are primarily disclosed herein, non-rechargeable(primary) electrochemical cells are intended to benefit from theinvention as well.

In some embodiments, alloys may be incorporated into the anode, and mayenhance the performance of the cell. For example, an alloy may beincorporated into an electroactive layer of the cell and mayadvantageously increase the efficiency of cell performance. Someelectrochemical cells (e.g., rechargeable batteries) may undergo acharge/discharge cycle involving deposition of metal (e.g., lithiummetal) on the surface of the anode upon charging and reaction of themetal on the anode surface, wherein the metal diffuses from the anodesurface, upon discharging. In some cases, the efficiency and uniformityof such processes may affect cell performance. The use of materials suchas alloys in an electroactive component of the cell have been found, inaccordance with aspects described herein, to increase the efficiency ofsuch processes and to increase the cycling lifetime of the cell. Forexample, the use of alloys may reduce the formation of dendrites on theanode surface and/or limit surface development.

Lithium metal alloys having the formula Li—Z may function well in anelectrochemical cell when low amounts of Z are present, i.e., the cellmay efficiently undergo charge-discharge cycling and/or may reduce orprevent formation of lithium dendrites or other compositions that mayform on the surface of an electrode. The additive, Z, may be anysuitable material capable of forming an alloy with lithium (or othersuitable electroactive metal). The term “alloy” is given its ordinarymeaning in the art, and refers to a combination (e.g., solid, solidsolution) of two or more elements, wherein at least one element is ametal, and wherein the resulting material has metallic properties.

In one specific set of embodiments, Z is a metal. In other embodiments,Z is a different material. In some cases, Z may be a semiconductor.Materials suitable for use as Z include, for example, a Group 1-17element, a Group 2-14 element, or a Group 2, 10, 11, 12, 13, 14, 15element. Suitable elements from Group 2 of the Periodic Table mayinclude beryllium, magnesium, calcium, strontium, barium, and radium.Suitable elements from Group 10 may include, for example, nickel,palladium, or platinum. Suitable elements from Group 11 may include, forexample, copper, silver, or gold. Suitable elements from Group 12 mayinclude, for example, zinc, cadmium, or mercury. Elements from Group 13that may be used in the present invention may include, for example,boron, aluminum, gallium, indium, or thallium. Elements from Group 14that may be used in the present invention may include, for example,carbon, silicon, germanium, tin, or lead. Elements from Group 15 thatmay be used in the present invention may include, for example, nitrogen,phosphorus, or bismuth. In some cases, Z is Al, Mg, Zn, or Si. In somecases, Z is Al. In other cases, Z is Mg.

Where Z is a metal, it is to be understood that one or more metals canbe used. Similarly, where Z is a semiconductor, one or moresemiconducting materials can be used. Additionally, metals andsemiconductors can be mixed. That is, Z can be a single metal, a singlesemiconductor, or one or more metals or one or more semiconductorsmixed. Non-limiting examples of suitable metals are listed above, andsuitable components of semiconductors are listed above. Those ofordinary skill in the art are well aware of semiconductors that can beformed from one or more of the elements listed above, or other elements.

In certain cases, Z is a nonmetal. For example, Z may be N, O, or C. Insome instances, N, O, C, or other nonmetals that may form an alloy withlithium are in the form of a gas (e.g., N₂, O₂, and CO₂) prior toforming an alloy with lithium. In embodiments where Z is a nonmetal, theLi—Z metal alloy may have a primary phase consisting essentially of Liand a secondary phase consisting essentially of Li_(X)Z_(y) and Z,wherein the secondary phase is substantially non-electricallyconducting.

In the following discussion, reference will be made to material (e.g.,“Z”) “substantially uniformly dispersed throughout a bulk portion of” amaterial, such as an anode (e.g., a base electrode material layer) oranother electrode. “Substantially uniformly dispersed,” in this context,means that, upon viewing a cross-sectional portion of any such material,where the cross-section may comprise the average makeup of a number ofrandom cross-sectional positions of the material, investigation of thematerial at a size specificity on the order of grains, or atoms, revealsessentially uniform dispersement of Z in the bulk material. For example,a photomicrograph, scanning electron micrograph, or other similarmicroscale or nanoscale investigative process will reveal essentiallyuniform distribution. “A bulk portion” of a material includes at least50% of a cross-sectional dimension of the material. In certainembodiments, a bulk portion may comprise at least 60%, 70%, 80%, 90%, or95% of a cross-sectional dimension of the material. Those of ordinaryskill in the art, with this description, will understand clearly themeaning of these terms.

Those of ordinary skill in the art can also determine the degree ofdispersion of a first material (e.g., Z) in a second material (e.g.,lithium) by diffusion calculations based on parameters such as the typeof materials, concentration/amounts and thicknesses of the materials,temperature, the time allowed for diffusion, etc. Generally, a very thinlayer of a first material on a second material will facilitate fasterdispersion of the first material into the second material (e.g., to forma uniformly dispersed layer of the two materials), compared to a thickerlayer of the first material on the second material. The degree ofdispersion also depends on the method of fabricating the materials. Forinstance, physical mixing and/or co-deposition of a first and a secondmaterial may form substantially uniformly dispersed materials prior tocharge or discharge of the cell, whereas in certain embodimentsinvolving layers of materials, the materials are not uniformly disperseduntil after a certain charge/discharge cycle. The latter may occurbecause charge and/or discharge of the cell can also facilitatedispersion. For instance, a first material is more likely to beuniformly dispersed within a second material after 20^(th) dischargethan after 1^(st) discharge of the cell.

As mentioned, Z may be substantially uniformly dispersed throughout abulk portion of an electrode, e.g., prior to assembly of the alloy ontoa substrate or prior to X^(th) discharge, as described herein. In otherembodiments, however, Z is not substantially uniformly dispersedthroughout a bulk portion of an electrode. For instance, Z may form agradient within the alloy or Z may be in the form of a layer on top of abulk portion of the electrode.

Accordingly, in some embodiments, Z is substantially uniformly dispersedthroughout a bulk portion of the anode (e.g., a base electrode materiallayer) prior to 10^(th) discharge. In some cases, Z is substantiallyuniformly dispersed throughout a bulk portion of the anode prior to5^(th) discharge, or, in some cases, prior to 3^(rd) discharge, or inother cases, prior to 1^(st) discharge. In yet other cases, Z issubstantially uniformly dispersed throughout a bulk portion of the anodeprior to 15^(th), 20^(th), or 25^(th) discharge.

It is also to be understood that “prior to X^(th) discharge”, or “havingbeen discharged less than X times” or the like, means at a time or timesprior to a point where a rechargeable electrochemical device has beencharged and discharged no more than X times, where charge meansessentially full charge, and discharge means, on average of alldischarges, at least 75% discharge.

In some cases, Z may be a metal or semiconductor that is present, in anelectrode, in an amount greater than 25 ppm, 50 ppm, 100 ppm, 200 ppm,300 ppm, 400 ppm or 500 ppm, but less than or equal to 1 wt %, 2 wt %, 5wt %, 10 wt %, 12 wt %, 15 wt %, or 20 wt % of the alloy or electrode.As used herein, “wt %” means percent by total weight of the alloy orelectrode itself, absent current collector, electrolyte and othermaterials.

As noted, certain electrochemical cells utilizing electrodes describedherein exhibit surprising performance characteristics. In oneembodiment, a rechargeable cell has a discharge capacity of at least1000, 1200, 1600, or 1800 mAh at the end of the cell's 15^(th), 25^(th),30^(th), 40^(th), 45^(th), 50^(th), or 60^(th) cycle. The dischargecapacity may be at least 2%, 5%, 7%, 10%, or 15% greater than that of asecond rechargeable cell of essentially identical composition anddimension but comprising a Li anode without Z. In one set ofembodiments, a rechargeable cell, including one of those described aboveor otherwise, is established such that there is a potential differencebetween its anode and that of the “second rechargeable cell” discussedabove that is less than 5, 10, or 15 mV.

Another measure of some of the surprising performance characteristics ofcertain electrodes described herein includes energy density (which canbe expressed as Watt Hours Per Kilogram (Wh/kg) or energy per size, asexpressed as Watt Hours Per Liter (Wh/l)). Various energy density andenergy per size characteristics exhibited by cells prior to X^(th)discharge, where X is any of the numbers described herein, include, forexample, at least 200, at least 250, at least 300, at least 350, atleast 400, at least 450, or at least 500 Wh/kg.

In one set of embodiments, the Li—Z alloy has a primary phase consistingessentially of Li and a secondary phase consisting essentially ofLi_(X)Z_(y), the secondary phase being substantially non-electricallyconducting. Where a multiple phase arrangement such as that describedimmediately above exists, the phase is typically usually distinguishableby SEM or other suitable technique and at least one of the phases has anaverage cross-sectional dimension in the range of, for example, 0.1-100microns, 0.5-50 microns, or, in some cases, 0.5-10 microns. Especiallyin connection with these embodiments, Z, in addition to being in one ormore of the materials described above, can be nitrogen, oxygen, orcarbon.

Additional arrangements, components, and advantages of alloys aredescribed in more detail in U.S. patent application Ser. No. 11/821,576,filed Jun. 22, 2007, entitled “Lithium Alloy/Sulfur Batteries”,published as U.S. Pub. No. 2008/0318128, which is incorporated herein byreference in its entirety.

In certain embodiments, the thickness of the anode may vary from, e.g.,about 2 to 200 microns. For instance, the anode may have a thickness ofless than 200 microns, less than 100 microns, less than 50 microns, lessthan 25 microns, less than 10 microns, or less than 5 microns. Thechoice of the thickness may depend on cell design parameters such as theexcess amount of lithium desired, cycle life, and the thickness of thecathode electrode. In one embodiment, the thickness of the anode activelayer is in the range of about 2 to 100 microns (e.g., about 5 to 50microns, about 5 to 25 microns, or about 10 to 25 microns).

The layers of an anode may be deposited by any of a variety of methodsgenerally known in the art, such as physical or chemical vapordeposition methods, extrusion, and electroplating. Examples of suitablephysical or chemical vapor deposition methods include, but are notlimited to, thermal evaporation (including, but not limited to,resistive, inductive, radiation, and electron beam heating), sputtering(including, but not limited to, diode, DC magnetron, RF, RF magnetron,pulsed, dual magnetron, AC, MF, and reactive), chemical vapordeposition, plasma enhanced chemical vapor deposition, laser enhancedchemical vapor deposition, ion plating, cathodic arc, jet vapordeposition, and laser ablation.

Deposition of the layers may be carried out in a vacuum or inertatmosphere to minimize side reactions in the deposited layers whichcould introduce impurities into the layers or which may affect thedesired morphology of the layers. In some embodiments, anode activelayers and the layers of multi-layered structures are deposited in acontinuous fashion in a multistage deposition apparatus.

Specifically, methods for depositing an electroactive material such aslithium onto a substrate include methods such as thermal evaporation,sputtering, jet vapor deposition, and laser ablation. Alternatively,where the anode comprises a lithium foil, or a lithium foil and asubstrate, these can be laminated together by a lamination process asknown in the art, to form an anode layer.

An anode, such as that shown in FIG. 2 and in other embodimentsdescribed herein, may include a single-ion conductive material layer 150as part of a multi-layered structure 122. In some embodiments, thesingle-ion conductive material is non-polymeric. In certain embodiments,the single-ion conductive material layer is defined in part or in wholeby a metal layer that is highly conductive toward lithium and minimallyconductive toward electrons. In other words, the single-ion conductivematerial may be one selected to allow lithium ions, but to impedeelectrons or other ions, from passing across the layer. The metal layermay comprise a metal alloy layer, e.g., a lithiated metal layerespecially in the case where a lithium anode is employed. The lithiumcontent of the metal alloy layer may vary from about 0.5% by weight toabout 20% by weight, depending, for example, on the specific choice ofmetal, the desired lithium ion conductivity, and the desired flexibilityof the metal alloy layer. Suitable metals for use in the single-ionconductive material include, but are not limited to, Al, Zn, Mg, Ag, Pb,Cd, Bi, Ga, In, Ge, Sb, As, and Sn. Sometimes, a combination of metals,such as the ones listed above, may be used in a single-ion conductivematerial.

In other embodiments, the single-ion conductive material may include aceramic layer, for example, a single ion conducting glass conductive tolithium ions. Suitable glasses include, but are not limited to, thosethat may be characterized as containing a “modifier” portion and a“network” portion, as known in the art. The modifier may include a metaloxide of the metal ion conductive in the glass. The network portion mayinclude a metal chalcogenide such as, for example, a metal oxide orsulfide. Single-ion conductive layers may include glassy layerscomprising a glassy material selected from the group consisting oflithium nitrides, lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium oxides (e.g., Li₂O,LiO, LiO₂, LiRO₂, where R is a rare earth metal), lithium lanthanumoxides, lithium titanium oxides, lithium borosulfides, lithiumaluminosulfides, and lithium phosphosulfides, and combinations thereof.In one embodiment, the single-ion conductive layer comprises a lithiumphosphorus oxynitride in the form of an electrolyte.

The thickness of a single-ion conductive material layer (e.g., within amulti-layered structure) may vary over a range from about 1 nm to about10 microns. For instance, the thickness of the single-ion conductivematerial layer may be between 1-10 nm thick, between 10-100 nm thick,between 100-1000 nm thick, between 1-5 microns thick, or between 5-10microns thick. The thickness of a single-ion conductive material layermay be no greater than, e.g., 10 microns thick, no greater than 5microns thick, no greater than 1000 nm thick, no greater than 500 nmthick, no greater than 250 nm thick, no greater than 100 nm thick, nogreater than 50 nm thick, no greater than 25 nm thick, or no greaterthan 10 nm thick. In some cases, the single-ion conductive layer has thesame thickness as a polymer layer in a multi-layered structure.

The single-ion conductive layer may be deposited by any suitable methodsuch as sputtering, electron beam evaporation, vacuum thermalevaporation, laser ablation, chemical vapor deposition (CVD), thermalevaporation, plasma enhanced chemical vacuum deposition (PECVD), laserenhanced chemical vapor deposition, and jet vapor deposition. Thetechnique used may depend on the type of material being deposited, thethickness of the layer, etc.

In some embodiments, single-ion conducting layers can be treated with apolymer or other material such that pinholes and/or nanopores of thesingle-ion conducting layers may be filled with the polymer. Suchcomposite structures can impede the diffusion of certain species (e.g.,electrolyte and/or polysulfides) towards the anode, e.g., by increasingthe distance, and tortuosity, through which such a species would need topass to penetrate the entire multi-layer arrangement to arrive at theanode.

In one embodiment, a single-ion conductive layer is infiltrated with amonomeric precursor of the transport-inhibiting substance, so that theporous structure is effectively filled with the monomer, the monomerbeing driven into the nanoporous regions of the porous single-ionconductive layer by the high surface energy present on the single-ionconductive layer's internal surfaces. The single-ion conductive materialmay be treated with an activation process before treatment with themonomer, so that surface energy within the material becomes unusuallyhigh, relative to that achievable in normal atmospheric processes.

In some instances, monomer vapor can be condensed onto the single-ionconductive material layer, whereby it is then able to wick along theinternal surfaces of the single-ion conductive material layer, untilall, or some useful portion of, such available tortuous by-paths ofpermeation are filled by the monomer. A subsequent curing step, eitherphoto-initiated techniques, plasma treatment, or an electron beam, canthen be introduced for polymerization of the infiltrated monomer. Theparticular cure method utilized will depend on the specific choice ofmaterials and the layer thickness, amongst other variables.

Suitable material used as the transport-inhibiting substance includesmaterial known to fully or partially inhibit (or determined to inhibitthrough simple screening) transport of a particular unwanted speciesthrough the material. As mentioned, material may also be selectedaccording to physical properties, including properties addingflexibility and/or strength to the overall material with which it iscombined. Specific examples of materials include, as noted, polymersdescribed herein for use as layers in the multi-layered structure,and/or other polymeric or other species. Where hydrophobicity isdesirably added to the overall arrangement, one way to do so is to usean infiltrating transport-inhibiting substance having some degree ofhydrophobic character.

Formation of composite single-ion conductive structures may beaccomplished by a variety of means; however, in some embodiments, thestructure is formed by vacuum vapor deposition methods and apparatusreadily available in prior art manufacturing processes. Accordingly,composite structures may be formed utilizing a variety of prior artvapor sources such as sputtering, evaporation, electron-beamevaporation, chemical vapor deposition (CVD), plasma-assisted CVD, etc.The monomer vapor source may similarly be any suitable monomer vaporsource of the prior art, including but not limited to flash evaporation,boat evaporation, Vacuum Monomer Technique (VMT), polymer multilayer(PML) techniques, evaporation from a permeable membrane, or any othersource found effective for producing a monomer vapor. For example, themonomer vapor may be created from various permeable metal frits, aspreviously in the art of monomer deposition. Such methods are taught inU.S. Pat. No. 5,536,323 (Kirlin) and U.S. Pat. No. 5,711,816 (Kirlin),amongst others.

As described herein, a multi-layered structure can include one or morepolymer layers. The thickness of a polymer layer (e.g., within amulti-layered structure) may vary over a range from about 0.1 microns toabout 10 microns. For instance, the thickness of the polymer layer maybe between 0.1-1 microns thick, between 1-5 microns thick, or between5-10 microns thick. The thickness of a polymer layer may be no greaterthan, e.g., 10 microns thick, no greater than 5 microns thick, nogreater than 2.5 microns thick, no greater than 1 micron thick, nogreater than 0.5 microns thick, or no greater than 0.1 microns thick.

In some embodiments including a multi-layered structure having more thanone polymer layer, the thicknesses of the polymer layers can vary withinthe structure. For instance, in some cases, the polymer layer closest tothe base electrode material layer (e.g., a Li reservoir) is thicker thanthe other polymer layers of the structure. This embodiment can, forexample, stabilize the anode by allowing lithium ions to plate out moreuniformly across the surface of the anode during charge.

In some embodiments, a polymer layer includes a polymer that isconductive to single ions but is also substantially electricallyconductive. Examples of such materials include electrically conductivepolymers (also known as electronic polymers or conductive polymers) thatare doped with lithium salts (e.g., LiSCN, LiBr, LiI, LiClO₄, LiAsF₆,LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆, LiC(SO₂CF₃)₃, andLiN(SO₂CF₃)₂). Conductive polymers are known in the art; examples ofsuch polymers include, but are not limited to, poly(acetylene)s,poly(pyrrole)s, poly(thiophene)s, poly(aniline)s, poly(fluorene)s,polynaphthalenes, poly(p-phenylene sulfide), and poly(para-phenylenevinylene)s. Electrically-conductive additives may also be added topolymers to form electrically-conductive polymers. Certain electricallyconductive materials may have a conductivity of, e.g., greater than 10⁻²S/cm, greater than 10⁻¹ S/cm, greater than 1 S/cm, greater than 10¹S/cm, greater than 10² S/cm, greater than 10³ S/cm, greater than 10⁴S/cm, or greater than 10⁵ S/cm.

In some embodiments, a polymer layer is conductive to one or more typesof ions, but is substantially non-electrically conductive. Examples ofion-conductive species that are substantially non-electricallyconductive include non-electrically conductive materials (e.g.,electrically insulating materials) that are doped with lithium salts.E.g., acrylate, polyethyleneoxide, silicones, polyvinylchlorides, andother insulating polymers that are doped with lithium salts can beion-conductive but substantially non-electrically conductive.

In some embodiments, single-ion conductive materials can also includenon-polymeric materials. Certain non-electrically conductive materialsmay have a resistivity of, e.g., greater than 10³ ohm-cm, greater than10⁴ ohm-cm, greater than 10⁵ ohm-cm, greater than 10⁶ ohm-cm, greaterthan 10⁷ ohm-cm, or greater than 10⁸ ohm-cm.

In some embodiments, suitable polymer layers for use in a multi-layeredstructure include polymers that are highly conductive towards lithiumand minimally conductive towards electrons. Examples of such polymersinclude ionically conductive polymers, sulfonated polymers, andhydrocarbon polymers. The selection of the polymer will be dependentupon a number of factors including the properties of electrolyte andcathode used in the cell. Suitable ionically conductive polymers mayinclude, e.g., ionically conductive polymers known to be useful in solidpolymer electrolytes and gel polymer electrolytes for lithiumelectrochemical cells, such as, for example, polyethylene oxides.Suitable sulfonated polymers may include, e.g., sulfonated siloxanepolymers, sulfonated polystyrene-ethylene-butylene polymers, andsulfonated polystyrene polymers. Suitable hydrocarbon polymers mayinclude, e.g., ethylene-propylene polymers, polystyrene polymers, andthe like.

Polymer layers of a multi-layered structure can also include crosslinkedpolymer materials formed from the polymerization of monomers such asalkyl acrylates, glycol acrylates, polyglycol acrylates, polyglycolvinyl ethers, polyglycol divinyl ethers, and those described in U.S.Pat. No. 6,183,901 to Ying et al. of the common assignee for protectivecoating layers for separator layers. For example, one such crosslinkedpolymer material is polydivinyl poly(ethylene glycol). The crosslinkedpolymer materials may further comprise salts, for example, lithiumsalts, to enhance ionic conductivity. In one embodiment, the polymerlayer of the multi-layered structure comprises a crosslinked polymer.

Other classes polymers that may be suitable for use in a polymer layerinclude, but are not limited to, polyamines (e.g., poly(ethylene imine)and polypropylene imine (PPI)); polyamides (e.g., polyamide (Nylon),poly(ϵ-caprolactam) (Nylon 6), poly(hexamethylene adipamide) (Nylon66)), polyimides (e.g., polyimide, polynitrile, andpoly(pyromellitimide-1,4-diphenyl ether) (Kapton)); vinyl polymers(e.g., polyacrylamide, poly(2-vinyl pyridine), poly(N-vinylpyrrolidone),poly(methylcyanoacrylate), poly(ethylcyanoacrylate),poly(butylcyanoacrylate), poly(isobutylcyanoacrylate), poly(vinylacetate), poly (vinyl alcohol), poly(vinyl chloride), poly(vinylfluoride), poly(2-vinyl pyridine), vinyl polymer, polychlorotrifluoroethylene, and poly(isohexylcynaoacrylate)); polyacetals; polyolefins(e.g., poly(butene-1), poly(n-pentene-2), polypropylene,polytetrafluoroethylene); polyesters (e.g., polycarbonate, polybutyleneterephthalate, polyhydroxybutyrate); polyethers (poly(ethylene oxide)(PEO), poly(propylene oxide) (PPO), poly(tetramethylene oxide) (PTMO));vinylidene polymers (e.g., polyisobutylene, poly(methyl styrene),poly(methylmethacrylate) (PMMA), poly(vinylidene chloride), andpoly(vinylidene fluoride)); polyaramides (e.g., poly(imino-1,3-phenyleneiminoisophthaloyl) and poly(imino-1,4-phenylene iminoterephthaloyl));polyheteroaromatic compounds (e.g., polybenzimidazole (PBI),polybenzobisoxazole (PBO) and polybenzobisthiazole (PBT));polyheterocyclic compounds (e.g., polypyrrole); polyurethanes; phenolicpolymers (e.g., phenol-formaldehyde); polyalkynes (e.g., polyacetylene);polydienes (e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene);polysiloxanes (e.g., poly(dimethylsiloxane) (PDMS),poly(diethylsiloxane) (PDES), polydiphenylsiloxane (PDPS), andpolymethylphenylsiloxane (PMPS)); and inorganic polymers (e.g.,polyphosphazene, polyphosphonate, polysilanes, polysilazanes).

The polymer materials listed above and described herein may furthercomprise salts, for example, lithium salts (e.g., LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂), to enhance ionic conductivity.

A polymer layer may be deposited by method such as electron beamevaporation, vacuum thermal evaporation, laser ablation, chemical vapordeposition, thermal evaporation, plasma assisted chemical vacuumdeposition, laser enhanced chemical vapor deposition, jet vapordeposition, and extrusion. The polymer layer may also be deposited byspin-coating techniques. A method for depositing crosslinked polymerlayers includes flash evaporation methods, for example, as described inU.S. Pat. No. 4,954,371 to Yializis. A method for depositing crosslinkedpolymer layers comprising lithium salts may include flash evaporationmethods, for example, as described in U.S. Pat. No. 5,681,615 toAfftnito et al. The technique used for depositing polymer layers maydepend on the type of material being deposited, the thickness of thelayer, etc.

As noted in the description with respect to FIG. 2 thus far, in oneparticular embodiment, the protective structure separating baseelectrode material layer 120 from electrolyte 160 includes a polymerlayer adjacent the base electrode material layer or separation layer130. In other arrangements, a polymer layer need not be the first layeradjacent the base electrode material layer or separation layer. Variousarrangements of layers, including various multi-layered structures, aredescribed below in which the first layer adjacent the base electrodematerial layer may or may not be polymeric. It is to be understood thatin all arrangements where any particular arrangement of layers is shown,alternate ordering of layers is within the scope of the invention.Notwithstanding this, one aspect of the invention includes theparticular advantages realized by a non-brittle polymer immediatelyadjacent the base electrode material layer or separation layer.

In some embodiments, multi-layered structures protect the base electrodematerial layer better than any individual layer that is included in thestructure. For instance, each of the layers of a multi-layeredstructure, e.g., the single-ion conducting layers, the polymer layers,or the separation layer, may possess desirable properties, but at thesame time may be most effective when complemented by other componentswith different properties. For example, single-ion conducting layers,especially vacuum deposited single-ion conducting layers, may beflexible as thin films, but when deposited as thicker layers, mayinclude defects such as pinholes and/or roughness, and may crack whenhandled. Polymer layers, and especially crosslinked polymer layers, forexample, can provide very smooth surfaces, may add strength andflexibility, and may be electron insulating, but may pass certainsolvents and/or liquid electrolytes. Accordingly, these are examples oflayers that can complement each other in an overall improved protectivestructure.

A multi-layered electrode stabilization or protection structure mayprovide many advantages over existing electrode protective structures.In much of the description herein, the structure is referred to as an“anode stabilization” structure, but it is to be understood that thestructure can be used for any electrode under suitable conditions aswould be understood by those of ordinary skill in the art when takinginto consideration the function of a particular electrode. Multi-layeredelectrode stabilization structures described herein, according tocertain embodiments, are designed to minimize defects that mightotherwise exist inherently in prior electrode protective structures, orthat might exist inherently in electrode protective structures using thesame or similar materials as those used in protective structuresdescribed herein, but arranged differently. For example, singleion-conductive layers (or other components of a device as describedherein) may include pinholes, cracks and/or grain boundary defects. Oncethese defects are formed, they can grow/propagate through the entirethickness of the film as the film grows and may become worse as the filmgrows thicker. By separating thin single ion-conductive layers from eachother with thin, pinhole free, smooth polymer layers, the defectstructure in each single ion-conductive layer can be decoupled from thedefect structure in every other single ion-conductive layer by anintervening polymer layer. Thus, at least one or more of the followingadvantages are realized in such a structure: (1) it is less likely fordefects in one layer to be directly aligned with defects in anotherlayer, and typically any defect in one layer is substantiallynon-aligned with a similar defect in another layer; (2) any defects inone single ion-conductive layer typically are much smaller and/or lessdetrimental than they would otherwise be in a thicker layer of otherwisesimilar or identical material. Where alternating single-ion conductivelayers and polymer layers are deposited atop each other in a fabricationprocess, each single-ion conductive layer has a smooth, pinhole free,polymer surface upon which to grow. In contrast, where the single-ionconductive layer to be deposited atop another single-ion conductivelayer (or continuously deposited as a single, thicker layer), defects inan underlying layer can serve to instigate defects in growth in a layerdeposited atop an underlying layer. That is, whether a protectivestructure is built with thicker single-ion conductive layers or multiplesingle-ion conductive layers atop each other, defects can propagatethrough the thickness, or from layer to layer, as the structure grows,resulting in larger defects, and defects that propagate directly orsubstantially directly throughout the entire structure. In this andother arrangements, the single ion-conductive layers can also grow withfewer defects than would occur if they were deposited directly onto therougher Li or electrolyte layers, particularly where the arrangement ofFIG. 2 is employed in which the first electrode stabilization layeraddressing the electrode is the polymer layer. Accordingly, in this andother arrangements, ion-conductive layers can be made that have overallfewer defects, defects that are not aligned with defects in nearestother ion-conductive layers and, where defects exist, they are typicallysignificantly less detrimental (e.g., smaller) than would otherwiseexist in a continuously-grown, thicker structure or layers of the sameor similar material deposited on top of each other.

A multi-layered electrode stabilization structure can act as a superiorpermeation barrier by decreasing the direct flow of species (e.g.,electrolyte and polysulfide species) to the base electrode materiallayer, since these species have a tendency to diffuse through defects oropen spaces in the layers. Consequently, dendrite formation, selfdischarge, and loss of cycle life can be reduced.

Another advantage of a multi-layered structure includes the mechanicalproperties of the structure. The positioning of a polymer layer adjacenta single-ion conductive layer can decrease the tendency of thesingle-ion conductive layer to crack, and can increase the barrierproperties of the structure. Thus, these laminates may be more robusttowards stress due to handling during the manufacturing process thanstructures without intervening polymer layers. In addition, amulti-layered structure can also have an increased tolerance of thevolumetric changes that accompany the migration of lithium back andforth from the base electrode material layer during the cycles ofdischarge and charge of the cell.

The ability of certain species that can be damaging to the baseelectrode material layer (e.g., electrolytes and/or polysulfides) toreach the base electrode material layer can also be decreased byproviding repeated layers of single-ion conductive layers and polymerlayers in a multi-layered structure. When a species encounters adefect-free portion of a single-ion conductive layer, transport of thespecies towards the base electrode material layer is possible if thespecies diffuses laterally through a very thin polymer layer toencounter a defect in a second single-ion conductive layer. Sincelateral diffusion through ultra-thin layers is very slow, as the numberof single-ion conductive/polymer layer pairs increases, the rate ofdiffusion of species becomes extremely small (e.g., the amount ofpenetration across the layer decreases). For instance, in oneembodiment, permeation of a species through polymer/single-ionconductive/polymer 3-layer structures can be reduced by three orders ofmagnitude over a single single-ion conductive layer alone (e.g., eventhough layers alone may have poor barrier properties). In anotherembodiment, a polymer/single-ion conductive/polymer/single-ionconductive/polymer 5-layer structure may have more than five orders ofmagnitude reduction of permeation of a species compared to that in asingle single-ion conductive layer. By contrast, permeation of the samespecies through a double-thick single-ion conductive layer may actuallyincrease. These significant reductions in permeation of destructivespecies through the electrode stabilization layer can increase as thenumber of layers increases where the thickness of individual layersdecreases. That is, in comparison to a two-layer structure of asingle-ion conductive layer and polymer layer of a particular, overallthickness, a ten-layer structure of alternating single-ion conductivelayers and polymer layers of the same overall thickness can varysignificantly decreased permeation of unwanted species through thelayer. Because of the significant advantage realized by the electrodestabilization protection structures described herein, overall loweramounts of material can be used in a particular protective structure, ascompared to prior art structures. Accordingly, at a particular level ofelectrode protection needed in a particular battery arrangement, asignificantly smaller mass of overall electrode stabilization materialscan be employed, significantly reducing overall battery weight.

A multi-layered structure can include various numbers ofpolymer/single-ion conductive pairs as needed. Generally, amulti-layered structure can have n polymer/single-ion conductive pairs,where n can be determined based on a particular performance criteria fora cell. E.g., n can be an integer equal to or greater than 1, or equalto or greater than 2, 3, 4, 5, 6, 7, 10, 15, 20, 40, 60, 100, or 1000,etc. In some embodiments, a multi-layered structure can include greaterthan 4, greater than 10, greater than 25, greater than 50, greater than100, greater than 200, greater than 500, greater than 1000, greater than2000, greater than 3000, greater than 5000, or greater than 8000polymer/single-ion conductive pairs. For example, in one particularembodiment, greater than 10,000 polymer/single-ion conductive pairs werefabricated.

FIG. 3 shows an example of a multi-layered electrode stabilizationstructure including multiple polymer and single-ion conductive layers.In the embodiment illustrated in FIG. 3, anode 111 includes baseelectrode material layer 120 (e.g., comprising an electroactive materialsuch as lithium), and multi-layered structure 124 positioned between thebase electrode material layer and an electrolyte 160 of the cell. Themulti-layered structure comprises at least two first layers each of asingle-ion conductive material and at least two second layers each of apolymeric material. For example, multi-layered structure 124 includespolymer layers 140 and 142, and single-ion conductive layers 150 and152. As shown in FIG. 3, the two layers of polymeric material and twolayers of single-ion conductive material are arranged in alternatingorder with respect to each other. Anode 111 may optionally comprise aseparation layer (e.g., a plasma treated layer) between the baseelectrode material layer and the polymeric layer (not shown in FIG. 3;illustrated in FIG. 2).

Anode 111 can also include additional multi-layered structures such asmulti-layered structure 126, comprising polymer layers 144 and 146, andsingle-ion conductive layers 154 and 156. Multi-layered structures 124and 126 can be combined to form a single multi-layered, or can beconstructed together as one, unitary multi-layered structure, includingfour layers each of a single-ion conductive material and for layers eachof a polymeric material. In other embodiments, structures can includeother numbers of alternating single-ion conductive layers and polymerlayers. For instance, a multi-layered structure may include n firstlayers each of a single-ion conductive material and n second layers eachof a polymeric material, in alternating arrangement, where n is greaterthan or equal to 2. E.g., n may equal at least 2, 3, 4, 5, 6, or 7, 10,15, 20, 40, 60, 100, etc.

In other embodiments, a multi-layered structure may include a greaternumber of polymer layers than single-ion conductive layers, or a greaternumber of single-ion conductive layers than polymer layers. For example,a multi-layered structure may include a n polymer layers and n+1single-ion conductive layers, or n single-ion conductive layers and n+1polymer layers, where n is greater than or equal to 2. E.g., n may equal2, 3, 4, 5, 6, or 7, etc. However, as described above, it is immediatelyadjacent at least one polymer layer and, in at least 50%, 70%, 90%, or95% of the ion-conductive layers, such layers are immediately adjacent apolymer layer on either side.

As mentioned, multi-layered electrode stabilization structures canprovide significant advantage where a particular amount of materialsdefining the structure are arranged in thinner, and greater numbers of,form. In some embodiments, each layer of the multi-layered structure hasa maximum thickness of less than 100 microns, less than 50 microns, lessthan 25 microns, less than 10 microns, less than 1 micron, less than 100nanometers, less than 10 nanometers, or less than 1 nanometer.Sometimes, the thickness of a single type of layer may be the same in amulti-layered structure. For instance, polymer layers 140 and 142 ofFIG. 3 may have the same thickness in multi-layered structure 124. Inother embodiments, the thickness of a single type of layer may bedifferent in a multi-layered structure, e.g., polymer layers 140 and 142may have different thicknesses in multi-layered structure 124. Thethicknesses of different types of layers in a multi-layered structuremay be the same in some cases, or different in other cases. For example,the thicknesses of polymer layers 140 and 142 may be different than thethickness of single-ion conductive layers 150 and 152. Those of ordinaryskill in the art can select appropriate materials and thicknesses oflayers in combination with the description herein.

A multi-layered structure may have various overall thicknesses that candepend on, for example, the electrolyte, the cathode, or the particularuse of the electrochemical cell. In some cases, a multi-layeredstructure can have an overall thickness of less than or equal to 1 cm,less than or equal to 5 mm, less than or equal to 1 mm, less than orequal to 700 microns, less than or equal to 300 microns, less than orequal to 250 microns, less than or equal to 200 microns, less than orequal to 150 microns, less than or equal to 100 microns, less than orequal to 75 microns, or less than or equal to 50 microns. It may also bedesirable to have a multi-layered structure having a certain thicknesswith a certain number of polymer/single-ion conductive material pairs.For instance, in one embodiment, a multi-layered structure may have athickness of less than 1 mm, and may include greater than 10polymer/single-ion conductive material pairs. In another embodiment, amulti-layered structure may have a thickness of less than 0.5 mm, andmay include greater than 50 polymer/single-ion conductive materialpairs. It is to be understood that a variety of embodiments may beprovided, each including specific combinations of overall electrodestabilization thickness, thicknesses of individual layers, numbers ofindividual layers, etc. as described herein.

Another embodiment described herein includes an embedded layer (e.g., ofa protective layer such as a single-ion conductive material layer)positioned between two layers of base electrode materials. This isreferred to as a “lamanode” structure. FIG. 4 shows an exemplary anode112 including a first layer of a base electrode material layer 120(e.g., lithium, also referred to as a Li reservoir), embedded layer 170,and a second layer 123 comprising the base electrode material (a workingLi layer). As illustrated in the embodiment shown in FIG. 4, the secondlayer is positioned between base electrode material layer 120 andelectrolyte 160. The second layer may be either in direct contact withthe electrolyte, or in indirect contact with the electrolyte throughsome form of a surface layer (e.g., an electrode stabilization ormulti-layered structure such as one described herein). The function ofthe bi-layer anode structure, with each base electrode material layerseparated by an embedded layer 170, will become clearer from thedescription below. It is noted that although layer 170 is illustratedand described as “embedded” in this description, it is noted that thelayer need not be partially or fully embedded. In many or most cases,layer 170 is a substantially thin, two-sided structure coated on eachside by base electrode material, but not covered by base electrodematerial at its edges.

In general, in operation of the arrangement shown in FIG. 4, some or allof second layer 123 of the anode is “lost” from the anode upon discharge(when it is converted to lithium ion which moves into the electrolyte).Upon charge, when lithium ion is plated as lithium metal onto the anode,it is plated as portion 123 (or at least some portion of second layer123) above layer 170. Those of ordinary skill in the art are aware thatin electrochemical cells such as those described herein, there is asmall amount of overall lithium loss on each charge/discharge cycle ofthe cell. In the arrangement illustrated in FIG. 4, the thickness oflayer 123 (or the mass of layer 123) can be selected such that most orall of layer 123 is lost upon full discharge of the cell (full“satisfaction” of the cathode; the point at which the cathode can nolonger participate in a charging process due to limitations that wouldbe understood by those of ordinary skill in the art).

In certain embodiments, layer 170 is selected to be one that isconductive to lithium ions. The embedded layer can shield the bottom Lilayer from damage as the high Li⁺ flux of the first cycle damages thetop Li layer surface. Accordingly, once all of layer 123 is consumed ina particular discharge cycle, further discharge results in oxidation oflithium from layer 120, passage of lithium ion through layer 170, andrelease of lithium ion into the electrolyte. Of course, layer 123 neednot be of a particular mass such that all or nearly all of it isconsumed on first discharge. It may take several discharge/chargecycles, and inherent small amount of lithium loss through each cycle, toresult in the need to draw lithium from section 120 through layer 170and into the electrolyte. But once that occurs, then each subsequentcharge/discharge cycle will generally progress as follows.

In certain embodiments, through most of a discharge cycle lithium willbe removed from section 123 and, at the very end of the discharge cycle,a small amount of lithium may be required to be drawn from section 120through layer 170 to make up for the amount of lithium lost in the mostrecent charge/discharge cycle. Upon charge, lithium may be plated uponlayer 170 as material 123 in an amount very slightly less than thatremoved from the anode during discharge. The embedded layer, which maybe an electrode stabilization layer, can be made of any suitablematerial selected, by those of ordinary skill in the art, in accordancewith the function described herein. Generally, layer 170 will be made ofa material that is single-ion conductive but that will not allow lithiummetal itself to pass. In some embodiments the material isnon-electrically-conductive, for reasons described below.

The ratio of the thickness of first and second layers of base electrodematerials can be calculated based on, e.g., a required “depth ofdischarge” (amount of lithium metal consumed) of the first discharge.The ratio may be, for instance, between the range of 0.2 to 0.4. Thethickness of anode 20 may be, for instance, less than 100 microns, lessthan 50 microns, less than 25 microns, or less than 10 microns. In someembodiments, anode 20 can have a thickness between 10 and 30 microns.

In some embodiments, embedded layer 170 may have a thickness between0.01-1 microns, and may depend on, e.g., the type of material used toform the embedded layer and/or the method of depositing the material.For example, the thickness of the embedded layer may be between 0.01-0.1microns, between 0.1-0.5 microns, or between 0.5-1 micron. In otherembodiments, thicker embedded layers are included. For example, theembedded layer can have a thickness between 1-10 microns, between 10-50microns, or between 50-100 microns. In some cases, the embedded materialcan be formed of a polymer, e.g., including ones listed above that arelithium ion conductive. The polymer film can be deposited usingtechniques such as vacuum based PML, VMT or PECVD techniques. In othercases, an embedded layer can comprise a metal or semi-conductormaterial. Metals and semi-conductors can be, for example, sputtered.Those of ordinary skill in the are can choose suitable materials,thicknesses, and methods of depositing embedded layers based on routineexperimentation in combination with disclosure herein.

In one embodiment, layer 170 is an anode stabilization structure ofmulti-layer form as described herein.

The second layer 123 of base electrode material layer can be used toprotect the surface of base electrode material layer 120 (e.g., a Lisurface) by limiting the current density-induced surface damage to athin (e.g., Li) layer above the embedded layer 170. For instance, layer123 can lithiate the cathode (be removed from the anode in the form oflithium ion) on the first cycle, e.g., under extremely high Li⁺ flux,instead of causing base electrode material layer 120 to lithiate thecathode, thereby protecting base electrode material layer 120. In eachcharge/discharge cycle (after the point is reached at which more lithiumthan is present in layer 123 is removed from the anode during discharge)only a small amount of lithium may be removed from section 120 and, insome embodiments, no lithium is re-plated at layer 120. This caneliminate or reducing the numbers of defects, cracks, pinholes and/ordendrites forming on the surface of base electrode material layer 120during the cathode lithiation. Anode 112 can improve the cycle life ofthe cell compared to a cell including an anode without a second layer ofLi and/or an embedded layer, as described in further detail below.

As mentioned, layer 170 should be able to pass lithium ions. It can bemade of material including ceramic, glass, or polymer layer (or amulti-layered structure, as described below) that is conductive to Liions and, in some embodiments, it substantially impedes the passage ofelectrons across the layer. By “substantially impedes”, in this context,it is meant that in this embodiment the material allows lithium ion fluxat least ten times greater than electron passage. As noted, in otherembodiments the material can be electron conductive.

Referring again to FIG. 4, anode 112 can function with any of a varietyof current collectors (not shown). Current collectors are well known tothose of ordinary skill in the art and can be readily selected fromsuitable materials based upon this disclosure. In one arrangement, acurrent collector addresses the bottom surface of layer 120 (the sideopposite electrolyte 160). In another arrangement, an edge collector isused, which can be positioned on one or multiple edges, i.e., a side(not shown), including layer 120, material 170, and layer 123. In otherarrangements, both a bottom collector and one or more edge collectorscan be used. Where only a bottom collector is used, material 170 shouldbe electronically conductive as well as lithium ion conductive. Where anedge collector is used material 170 can be selected to substantiallyinhibit electron passage.

In one particular set of embodiments, an edge collector is used andprovides advantages in anode stabilization/protection. One sucharrangement is illustrated in FIG. 5, where an embedded stabilizationstructure 124 (itself analogous to section 170 of FIG. 4), separatesanode 113 into one portion of a base electrode material layer 120 (e.g.,a Li reservoir), from a second portion of base electrode material layer123 (e.g., a working Li layer). The embedded layer, e.g., multi-layeredstructure 124, the Li reservoir, and layer 123 may, in some embodiments,all be electrically connected at the edge current collector 180. In thearrangement illustrated in FIG. 5, a bottom current collector is notused, although a bottom current collector may be used in otherembodiments.

During operation of an electrochemical cell as illustrated in FIG. 5, oranother cell including an embedded layer between two base electrodematerial layers and with an edge collector, during discharge, currententers the anode through the working Li/electrolyte interface. However,the embedded layer can substantially block electron current whileallowing passage of Li ions. For instance, the flow of electron current,as illustrated by the arrows in FIG. 5, may be substantially impededthrough the electrode stabilization layer, to layer 120 of the anode,and to one or more current collectors. Thus, a substantial amount orsubstantially all of the current can pass through the working Li layer123 to the edge collector 180, e.g., in the direction of arrow 184,while a much smaller portion (or essentially no electron flow) passesthrough stabilization material 124 to the Li reservoir 120 to the edgecollector, e.g., in the direction of arrows 182 and 189, or to a bottomcurrent collector (not shown) in the direction of arrows 186 and 188. Asnoted, in some embodiments, the working Li layer, prior to firstdischarge of the cell, comprises more active electrode species than isdepleted upon full discharge of the cell, e.g., as to satisfy thecathode upon cathode lithiation. E.g., the working Li layer may includean amount of Li, prior to first discharge of the cell, such that greaterthan 50%, greater than 70%, greater than 90%, or greater than 95% of theLi of the working layer 123 is electrochemically dissolved upon thefirst discharge.

On charging, lithium ion is plated, as lithium metal, at base electrodematerial layer 123, as described above in connection with FIG. 4. Sincethe electrolyte/working Li layer 123/edge collector 180 is the lowestresistance path for electron current, most current takes this path onceLi ion reaches the working Li layer and is reduced. Current densityinduced damage/corrosion is significantly minimized since any suchprocesses occur only or primarily at the electrolyte/working Li 123interface, while base electrode material layer 120 remains undamaged. Asnoted above in connection with FIG. 4, as the working Li layer graduallyloses a small percentage of Li during each cycle, this Li is replaced bya flow of Li ions across the embedded layer 124 and into theelectrolyte. This results in more even loss/re-plating of lithium duringdischarge/charge cycles, therefore minimizing damage/corrosion of theanode and, importantly, the damage/corrosion can be inhibited or made tobe essentially zero in Li reservoir 120. As a result, the Li reservoirdoes not degenerate into isolated Li islands surrounded by corrosionbyproducts, as can be the case with use of a single layer Li anode.

A variety of arrangements can be employed to encourage even plating oflithium at layer 123 during charge. For example, although in theembodiment illustrated in FIG. 5 it can be advantageous to formmulti-layer structure 124 to be substantially non-electricallyconductive overall, one or more layers of the structure can be made tobe electrically conductive to define a current collector component. Forexample, in multi-layer structure 124 one or more of the layers, forexample layer 152 closest to base electrode material layer 123 andelectrolyte 160, can be made somewhat or significantly electricallyconductive. In this way, during charge, even deposition of the firstvery thin layer of lithium on the anode can be made to occur essentiallyevenly across structure 124. Once a portion of lithium has beendeposited, then the electronic conductivity of lithium itself alsofacilitates further even deposition of material 123.

Additional arrangements, components, and advantages of multi-layerstructures are described in more detail in U.S. patent application Ser.No. 11/400,781, filed Apr. 6, 2006, published as U.S. Pub. No.2007/0221265, entitled “Rechargeable Lithium/Water, Lithium/AirBatteries”, which is incorporated herein by reference in its entirety.

A variety of materials and arrangements can be used in individualassemblies described and illustrated herein, or in all of theassemblies. It is to be understood that where a particular component orarrangement is described in connection with one embodiment or figure,that component or arrangement can be used in connection with any others.One example of such a structure is a separation layer, e.g., a temporaryprotective material layer or a plasma CO₂ treatment layer, positionedbetween the an anode layer and a polymer layer or a multi-layeredstructure. For example, in the embodiment shown in FIG. 2, layer 130 isa separation layer. It is to be understood that where a separation layer130 is used, the first layer adjacent the separation layer opposite thebase electrode material layer is described herein at times to beadjacent the base electrode material layer. This is because theseparation layer is optional. In all instances in which a layer isdescribed as being adjacent, or immediately adjacent an electrode (forexample the polymer layer 140 of FIG. 2), an intervening separationlayer can be used but need not be used. Separation layers may improvethe compatibility of the base electrode material (e.g., lithium) withlayers deposited on top of the base electrode material layer. Forexample, when a single-ion conductive layer is desired at the lithiuminterface, it is preferable to deposit this directly on the lithiumsurface. However, the precursors to, or components of, such aninterfacial layer may react with lithium to produce undesirableby-products or result in undesirable changes in the morphology of thelayers. By depositing a separation layer on the lithium surface prior todepositing the interfacial layer such as a multi-layer structure 124(FIG. 3), side reactions at the lithium surface may be eliminated orsignificantly reduced. For example, when an interfacial film of alithium phosphorus oxynitride, as described in U.S. Pat. No. 5,314,765to Bates, is deposited in a nitrogen atmosphere by sputtering of Li₃PO₄onto a lithium surface, the nitrogen gas may react with lithium to formlithium nitride (LiN₃) at the anode surface. By depositing a layer of aprotective material that can be “temporary”, e.g., copper over thelithium surface, the interfacial layer may be formed without theformation of lithium nitride. A “temporary” protective layer is one thatceases to be in existence or identifiable after some time afterconstruction of the device, for example after some period of use of thedevice. For example, a thin layer of copper as a separation layer 130positioned over a lithium base electrode material layer 120 may diffuseinto an alloy with the lithium base electrode material until, after aparticular period of time and/or use of the device, base electrodematerial layer 120 will be primarily lithium, with a trace of copper,but layer 130 will no longer exist or be identifiable.

A temporary protective material layer may include a material that iscapable of forming an alloy with lithium metal, or is capable ofdiffusing into, dissolving into, and/or blending with lithium metal,e.g., during electrochemical cycling of the cell and/or prior toelectrochemical cycling of the cell. The temporary protective materiallayer can act as a barrier layer to protect the lithium surface duringdeposition of other layers, such as during the deposition of amulti-layered structure on top of the base electrode material layer.Further, the temporary protective layer may allow transportation of thelithium films from one processing station to the next withoutundesirable reactions occurring at the lithium surface during assemblyof cells, or for solvent coating of layers onto the base electrodematerial layer.

The thickness of the temporary protective material layer is selected toprovide the necessary protection to the layer comprising lithium, forexample, during subsequent treatments to deposit other anode or celllayers. In some embodiments, it is desirable to keep the layer thicknessas thin as possible while providing the desired degree of protection soas to not add excess amounts of non-active materials to the cell whichwould increase the weight of the cell and reduce its energy density. Inone embodiment, the thickness of the temporary protective layer isbetween 5 to 500 nanometers, e.g., between 20 to 200 nanometers, between50 to 200 nanometers, or between 100 to 150 nanometers.

Suitable materials that may be used as temporary protective materiallayers include metals such as copper, magnesium, aluminum, silver, gold,lead, cadmium, bismuth, indium, gallium, germanium, zinc, tin, andplatinum.

In some cases, separation layer 130 can include plasma treated layerssuch as CO₂ or SO₂ induced layers. Plasma treated layers can allownearly the entire surface area of the base electrode material layer toparticipate in the current carrying process. In other words, plasmatreated layers may allow uniform current density across a surface anddecreases the amount of pitting on a surface. In some cases, thesetreatments alone routinely increase cycle life by 15% to 35% becausemore of the Li is available for use during discharge. The plasma surfacetreatments can make more of the Li available to be cycled by creating asurface that is substantially homogeneous in topography.

In some embodiments, electrodes described herein include an outer layer,e.g., a layer that is in contact with the electrolyte of the cell. Thisouter layer can be a layer such as stabilization layers 122, 124, 126,etc. as shown in the figures, or can be an auxiliary outer layerspecifically selected to interface directly with the electrolyte. Outerlayers may be selected for properties such as Li-ion conduction,electron conduction, protection of underlying layers which may beunstable to components present in the electrolyte, nonporous to preventpenetration by electrolyte solvents, compatible with electrolyte and theunderlying layers, and flexible enough to accommodate for volume changesin the layers observed during discharge and charge. The outer layershould further be stable and preferably insoluble in the electrolyte.

Examples of suitable outer layers include, but are not limited to,organic or inorganic solid polymer electrolytes, electrically andionically conducting polymers, and metals with certain lithiumsolubility properties. In one embodiment, the polymer of the outer layeris selected from the group consisting of electrically conductivepolymers, ionically conductive polymers, sulfonated polymers, andhydrocarbon polymers. Further examples of suitable polymers for use inthe outer layer of the electrodes described herein are those describedin U.S. Pat. No. 6,183,901 to Ying et al.

The electrodes and cells described herein may further comprise asubstrate, as is known in the art, on or adjacent the surface of a baseelectrode material layer opposite that of a multi-layer structure (ifpresent). Substrates are useful as a support on which to deposit thebase electrode material, and may provide additional stability forhandling of thin (e.g., lithium) film anodes during cell fabrication.Further, in the case of conductive substrates, a substrate may alsofunction as a current collector useful in efficiently collecting theelectrical current generated throughout the anode and in providing anefficient surface for attachment of electrical contacts leading to anexternal circuit. A wide range of substrates are known in the art ofelectrodes. Suitable substrates include, but are not limited to, thoseselected from the group consisting of metal foils, polymer films,metallized polymer films, electrically conductive polymer films, polymerfilms having an electrically conductive coating, electrically conductivepolymer films having an electrically conductive metal coating, andpolymer films having conductive particles dispersed therein. In oneembodiment, the substrate is a metallized polymer film. In otherembodiments, the substrate may be selected fromnon-electrically-conductive materials.

Certain existing methods of fabricating electrodes involve depositingelectrode components onto a substrate that is eventually incorporatedinto an electrochemical cell. The substrate is typically of sufficientthickness and/or formed of a suitable material in order to be compatiblewith the electrode fabrication process. For example, fabrication of anelectrode comprising lithium metal as an electroactive material mayinvolve vacuum deposition of lithium metal at relatively hightemperatures and high rates that would cause certain substrates tobuckle unless the substrate is made of a certain material or has asufficient thickness. Some substrates that are suitable for suchfabrication steps may, however, end up reducing the performance of thecell if the substrate is incorporated into the cell. For instance, thicksubstrates may prevent buckling and therefore allow the deposition of athick layer of an electroactive material, but may reduce the specificenergy density of the cell. Furthermore, certain substrates that areincorporated into the electrochemical cell may react adversely withchemical species during cycling. To remedy these issues, certainembodiments described herein may involve methods of fabricating anelectrode using a release layer to separate portions of the electrodefrom a carrier substrate, which can then be removed from the electrodeduring or after assembly of the electrode into an electrochemical cell.Advantageously, such a method can allow a larger variety of substratesand/or more extreme processing conditions to be used when fabricatingelectrodes compared to that when the substrate is incorporated into anelectrochemical cell. The removal of a substrate from an electrochemicalcell can also reduce the number adverse reactions that may occur in thecell during cycling.

In some embodiments described herein, an electrode or an electrochemicalcell includes one or more release layers. Release layers describedherein are constructed and arranged to have one or more of the followingfeatures: relatively good adhesion to a first layer (e.g., a currentcollector, or in other embodiments, a carrier substrate or other layer)but relatively moderate or poor adhesion to a second layer (e.g., acarrier substrate, or in other embodiments, a current collector or otherlayer); high mechanical stability to facilitate delamination withoutmechanical disintegration; high thermal stability; ability to withstandthe application of a force or pressure applied to the electrochemicalcell or a component of the cell during fabrication and/or during cyclingof the cell; and compatibility with processing conditions (e.g.,deposition of layers on top of the release layer, as well ascompatibility with techniques used to form the release layer). Releaselayers may be thin (e.g., less than about 10 microns) to reduce overallbattery weight if the release layer is incorporated into theelectrochemical cell. A release layer should also be smooth and uniformin thickness so as to facilitate the formation of uniform layers on topof the release layer. Furthermore, release layers should be stable inthe electrolyte and should not interfere with the structural integrityof the electrodes in order for the electrochemical cell to have a highelectrochemical “capacity” or energy storage capability (i.e., reducedcapacity fade). In some cases, release layers from two electrodeportions can be adhered together, optionally using an adhesion promoteras described in more detail below.

FIG. 6A shows an exemplary electrode assembly that includes a releaselayer. As shown in the illustrative embodiment of FIG. 6A, electrodeassembly 210 includes several layers that are stacked together to forman electrode 212 (e.g., an anode or a cathode). Electrode 212 can beformed by positioning the layers on a carrier substrate 220. Forexample, electrode 212 may be formed by first positioning one or morerelease layers 224 on a surface of carrier substrate 220. As describedin more detail below, the release layer serves to subsequently releasethe electrode from the carrier substrate so that the carrier substrateis not incorporated into the final electrochemical cell. To form theelectrode, an electrode component such as a current collector 226 can bepositioned adjacent the release layer on the side opposite the carriersubstrate. Subsequently, an electroactive material layer 228 may bepositioned adjacent current collector 26. Optionally, additional layerscan be positioned adjacent base electrode material layer 228 (e.g.,comprising an electroactive material such as lithium) as describedherein. For example, a multi-layered structure 230 that protects thebase electrode material from an electrolyte, may be positioned on asurface 229 of layer 228. The multi-layer structure can include, forexample, polymer layers 234 and 240, and single-ion conductive layers238 and 242.

After electrode assembly 210 has been formed, the carrier substrate 220may be released from the electrode through the use of release layer 224.Release layer 224 can be either released along with the carriersubstrate so that the release layer is not a part of the final electrodestructure, or the release layer may remain a part of the final electrodestructure as shown illustratively in FIG. 6B. The electrode structureshown in FIG. 6B, or other configurations derived therefrom, may beincorporated into an electrochemical cell described herein, e.g., asanode 15 of FIG. 1.

The positioning of the release layer during release of the carriersubstrate can be varied by tailoring the chemical and/or physicalproperties of the release layer. For example, if it is desirable for therelease layer to be part of the final electrode structure, as shown inFIG. 6B, the release layer may be tailored to have a greater adhesiveaffinity to current collector 226 relative to its adhesive affinity tocarrier substrate 220. On the other hand, if it is desirable for therelease layer to not be part of an electrode structure, the releaselayer may be designed to have a greater adhesive affinity to carriersubstrate 220 relative to its adhesive affinity to current collector226. In the latter case, when a peeling force is applied to carriersubstrate 220 (and/or to the electrode), the release layer is releasedfrom current collector 226 and remains on substrate 220.

In certain embodiments, carrier substrate 220 is left intact withelectrode 212 as a part of electrode assembly 210 after fabrication ofthe electrode, but before the electrode is incorporated into anelectrochemical cell. For instance, electrode assembly 210 may bepackaged and shipped to a manufacturer who may then incorporateelectrode 212 into an electrochemical cell. In such embodiments,electrode assembly 210 may be inserted into an air and/or moisture-tightpackage to prevent or inhibit deterioration and/or contamination of oneor more components of the electrode assembly. Allowing carrier substrate220 to remain attached to electrode 212 can facilitate handling andtransportation of the electrode. For instance, carrier substrate 220 maybe relatively thick and have a relatively high rigidity or stiffness,which can prevent or inhibit electrode 212 from distorting duringhandling. In such embodiments, carrier substrate can be removed by themanufacturer before, during, or after assembly of an electrochemicalcell.

Although FIG. 6A shows release layer 224 positioned between carriersubstrate 220 and current collector 226, in other embodiments therelease layer may be positioned between other components of anelectrode. For example, the release layer may be positioned adjacentsurface 229 of base electrode material layer 228, and the carriersubstrate may be positioned on the opposite side of the base electrodematerial layer (not shown). In some such embodiments, an electrode maybe fabricated by first positioning one or more release layers onto acarrier substrate. Then, if any protective layer(s) such asmulti-layered structure 230 is to be included, the protective layer(s)can be positioned on the one or more release layers. For example, eachlayer of a multi-layered structure may be positioned separately onto arelease layer, or the multi-layered structure may be pre-fabricated andpositioned on a release layer at once. The base electrode material layermay then be positioned on the multi-layered structure. (Of course, if aprotective layer such as a multi-layered structure is not included inthe electrode, the base electrode material layer can be positioneddirectly on the release layer.) Afterwards, any other suitable layerssuch as a current collector may be positioned on the base electrodematerial layer. To form the electrode, the carrier substrate can beremoved from the protective layer(s) (or the base electrode materiallayer where protective layers are not used) via the release layer. Therelease layer may remain with the electrode or may be released alongwith the carrier substrate.

It should be understood that when a portion (e.g., layer, structure,region) is “on”, “adjacent”, “above”, “over”, “overlying”, or “supportedby” another portion, it can be directly on the portion, or anintervening portion (e.g., layer, structure, region) also may bepresent. Similarly, when a portion is “below” or “underneath” anotherportion, it can be directly below the portion, or an intervening portion(e.g., layer, structure, region) also may be present. A portion that is“directly on”, “immediately adjacent”, “in contact with”, or “directlysupported by” another portion means that no intervening portion ispresent. It should also be understood that when a portion is referred toas being “on”, “above”, “adjacent”, “over”, “overlying”, “in contactwith”, “below”, or “supported by” another portion, it may cover theentire portion or a part of the portion.

It should be understood, therefore, that in the embodiments illustratedin FIGS. 6A and 6B and in other embodiments described herein, one ormore additional layers may be positioned between the layers shown in thefigures. For example, one or more additional layers may be positionedbetween current collector 226 and release layer 224, and/or one or moreadditional layers may be positioned between release layer 224 andcarrier substrate 220. Furthermore, one or more layers may be positionedbetween other components of the cell. For example, one or more primerlayers can be positioned between a current collector and a baseelectrode material layer (e.g., a positive or negative electroactivematerial) to facilitate adhesion between the layers. Examples ofsuitable primer layers are described herein and in International PatentApplication Serial No. PCT/US2008/012042, published as InternationalPublication No. WO 2009/054987, filed Oct. 23, 2008, and entitled“Primer For Battery Electrode”, which is incorporated herein byreference in its entirety. Furthermore, one or more layers such asplasma treatment layers may be deposited on surface 229 of baseelectrode material layer 228, optionally between the electroactivematerial layer and multi-layer structure 230.

Although FIGS. 6A and 6B show a single release layer 224 as part ofelectrode assembly 210, any suitable number of release layers may beused. For example, a release system may include 2, 3, 4 or more layers.The number of layers used in a release system may depend at least inpart on whether the release layer(s) is to be incorporated into thefinal electrochemical cell, or whether the release layer(s) is removedalong with the carrier substrate. For example, in some embodiments inwhich the release layer(s) is to be incorporated into theelectrochemical cell, a fewer number of release layer(s) may bedesirable (e.g., less than 3, or less than 2 release layers). This isbecause a fewer number of release layers can reduce the complexity ofthe fabrication process as well as reduce the weight of the overallelectrochemical cell, thereby increasing the specific energy density ofthe cell.

In other embodiments, however, more than one release layer is used tofabricate a component of an electrochemical cell. For instance, a firstrelease layer may be positioned adjacent a carrier substrate and mayhave, for example, a relatively high adhesive affinity to the carriersubstrate. The first release layer may be chosen because it iscompatible with certain processing conditions, but it may have arelatively high adhesive affinity to a second surface (e.g., currentcollector 226 of FIG. 6A). In such embodiments, the release layer wouldnot allow release of the carrier substrate. Thus, a second release layermay be positioned between the first release layer and the second surfaceto allow adequate release of the carrier substrate. In one embodiment,the second release layer has a relatively high adhesive affinity to thefirst release layer, but a relatively low adhesive affinity to thesecond surface. As such, the application of a force could allow removalof the carrier substrate and both release layers from the secondsurface. In another embodiment, the second release layer has arelatively low adhesive affinity to the first release layer andrelatively high adhesive affinity to the second surface. In suchembodiments, the application of a force could allow removal of thecarrier substrate and the first release layer, which the second releaselayer and the second surface remain intact. Other configurations ofrelease layers are also possible.

As shown in FIG. 6B, release layer 224 can be a part of the finalelectrode and/or electrochemical cell once fabricated. In someembodiments, release layer 224 provides essentially no electrochemical,structural and/or activational feature to the electrochemical cell afterbeing incorporated into the cell. For example, in some embodiments,release layer 224 does not substantially act as a separator, anelectroactive material, or a protective layer for an electroactivematerial, does not substantially contribute to the mechanical stabilityof the electrochemical cell, and/or does not substantially facilitatethe conduction of ions and/or electrons across the release layer. Thatis, the release layer may be substantially non-ionically conductiveand/or non-electrically conductive. In some cases, a release layer, onceincorporated into an electrochemical cell, does not act as anactivational feature such as maintaining two components of the cell outof contact until the cell is ready for use. As such, the release layermay have essentially no function other than to have releasecharacteristics allowing a first layer or component to be separated froma second layer or component during fabrication of the electrochemicalcell. As described herein, such a release layer having essentially noother function other than to act as a release layer may nevertheless beincorporated into the cell because the advantages of facilitating thefabrication process outweighs the potential negative effects ofincorporating the release layer into the cell (e.g., by reducingspecific energy density of the cell).

In other embodiments, a release layer does have one or more functionsonce incorporated into an electrochemical cell. For example, the releaselayer may act as a separator, an electroactive material, or a protectivelayer for an electroactive material, may contribute to the mechanicalstability of the electrochemical cell, and/or may facilitate theconduction of ions and/or electrons across the release layer.

In some particular embodiments, a release layer has an adhesive functionof allowing two components of an electrochemical cell to adhere to oneanother. One such example is shown in the embodiments illustrated inFIGS. 7A and 7B. As shown illustratively in FIG. 7A, a first electrodeportion 212A may include one or more release layers 224A, a currentcollector 226A, and an base electrode material layer 228A. Such anelectrode portion may be formed after being released from a carriersubstrate, e.g., using the method described above in connection withFIGS. 6A and 6B. Similarly, a second electrode portion 212B may includea release layer 224B, a current collector 226B, and an electroactivematerial layer 228B. Additional layers (e.g., protective multi-layeredstructures) can also be deposited onto surfaces 229A and/or 229B ofelectrode portions 212A and 212B respectively, as described above.

As shown in the embodiment illustrated in FIG. 7B, a back-to-backelectrode assembly 213 may be formed by joining electrode portions 212Aand 212B, e.g., via release layers 224A and 224B. The electrode portionsmay be separate, independent units or part of the same unit (e.g.,folded over). As illustrated in FIG. 7B, release layers 224A and 224Bare facing one another. In other embodiments, however, the electrodeportions can be stacked upon one another in series such that releaselayers 224A and 224B do not face one another in the final configuration.

Any suitable method may be used to join two components of anelectrochemical cell via one or more release layers. In someembodiments, release layers 224A and 224B are formed of one or morematerials that naturally have a relatively high adhesive affinity toeach other, e.g., either inherently or after being activated. In someembodiments, an adhesion promoter may be used to facilitate adhesion oftwo components. For example, the materials used to form the releaselayers may be joined by applying an external stimulus such as heatand/or light to activate a surface of a release layer to make it moreadhesive. In other embodiments, an adhesion promoter in the form of achemical such as a crosslinker can be applied to a surface of a releaselayer to facilitate joining with another layer. Adhesion promoters inthe form of solvents and/or adhesives can also be used, as described inmore detail below. In yet other embodiments, a release layer mayinherently have a high adhesive affinity to a material in which it is tobe joined and no adhesion promoter is needed. Pressure may optionally beapplied during the joining of two components.

In some embodiments, two components of an electrochemical cell such aselectrode portions 212A and 212B of FIG. 7A are joined with one anothervia a lamination process. A lamination process may involve, for example,applying an adhesion promoter such as a solvent (optionally containingother materials) to a surface of release layers 24A and/or 24B andsolvating at least a portion of the release layer(s) to make the releaselayers more susceptible to adhesion. The release layers can then bebrought together to join the release layers. After joining (or, in someembodiments, prior to joining), the solvent can be optionally removed,e.g., by a drying process. In some such embodiments, e.g., when releaselayers 224A and 224B are formed of the same material, the joining of therelease layers can result in a single layer 227, as shown in theembodiment illustrated in FIG. 7B. For instance, where release layers224A and 224B are formed of a polymeric material, the joining of therelease layers (e.g., after solvation) can cause polymer chains at thesurface of one release layer to intertwine with polymer chains at thesecond release layer. In some cases, intertwining of the polymer chainscan occur without the application of additional chemicals and/orconditions (e.g., without the use of an adhesion promoter). In otherembodiments, intertwining of polymer chain can be facilitated bysubjecting the polymer to certain conditions such as cross linking ormelting, as described in more detail below.

When first and second release layers are joined together (optionallyusing an adhesion promoter), the adhesive strength between the tworelease layers may be greater than the adhesive strength between thefirst release layer and a layer opposite the second release layer (e.g.,between the first release layer and the current collector). In otherembodiments, the adhesive strength between the two release layers may beless than the adhesive strength between the first release layer and alayer opposite the second release layer (e.g., between the first releaselayer and the current collector). Adhesive strengths can be determinedby those of ordinary skill in the art in combination with thedescription provided herein.

As described herein, in some embodiments, lamination may involveapplying an adhesion promoter (e.g., in the form of an adhesive or asolvent combination) to a surface of a release layer prior to joining ofthe two electrodes. For instance, an adhesive (e.g., a polymer or anyother suitable material) may be added to a solvent or solventcombination to form an adhesion promoter formulation, which is thenapplied uniformly to a surface of release layer 224A (and/or 224B). Whenapplying an adhesion promoter to the release layer(s), the adhesionpromoter may be applied to only one of the release layers, or to bothrelease layers. The two surfaces to be adhered can then be joined,optionally followed by the application of heat, pressure, light, orother suitable condition to facilitate adhesion.

As described in more detail below, an adhesion promoter may form adiscrete layer at the interface between the two release layers to bejoined (or between any two components to be joined). The layer ofadhesion promoter may, in some cases, be very thin (e.g., between 0.001and 3 microns thick), as described in more detail below. Advantageously,using a thin layer of adhesion promoter can increase the specific energydensity of the cell compared to using a thicker layer of adhesionpromoter.

In other embodiments, an adhesion promoter does not form a discretelayer at the interface between the two release layers. In some suchembodiments, the adhesion promoter is a solvent or solvent combinationthat wets the surface(s) of the release layer(s), and does not include apolymer and/or any other non-solvent material. The solvent in theadhesion promoter may solvate, dissolve, and/or activate portions of therelease layer surface to promote adhesion of the release layer withanother release layer.

In other embodiments in which an adhesion promoter does not form adiscrete layer at the interface between the two release layers, theadhesion promoter formulation may include a solvent or solventcombination that wets the surface(s) of the release layer(s) along witha polymer in relatively small amounts (e.g., less than 5%, less than 4%,less than 3%, less than 2%, or less than 1% by weight of the adhesionpromoter formulation).

In some cases in which the adhesion promoter includes a polymer (or anyother non-solvent material) in its formulation, the type, amount, andmolecular weight of the polymer (or other non-solvent material) may bechosen such that a discrete layer is not formed at the interface betweentwo release layers. For instance, even though the adhesion promoter maybe applied to the surface of the release layer in the form of a layer ora coating, after joining the release layers, the polymer or othernon-solvent material in the adhesion promoter formulation may migrateinto the pores or interstices of the release layer(s) or be misciblewith the release layer(s) such that a discrete layer of adhesionpromoter is not formed. In other embodiments, the polymer or non-solventmaterial of the adhesion promoter formulation may join with polymerchains of the release layer(s), and the joined polymer chains mayrearrange within the release layer(s) such that a discrete layer ofadhesion promoter is not formed. In some cases, such rearrangementand/or migration causes at least a portion of the adhesion promoter tobe interspersed (e.g., uniformly or non-uniformly) in the first and/orsecond release layers. In certain embodiments, a substantial portion(e.g., substantially all) of the adhesion promoter is interspersed(e.g., uniformly or non-uniformly) in the first and/or second releaselayers. In some embodiments, such rearrangement and/or migration occursupon assembly of the electrode or electrochemical cell. In otherembodiments, such rearrangement and/or migration occurs during cyclingof the electrochemical cell.

After assembly of the electrode and/or cell, all or portions of theadhesion promoter may be positioned between first and secondelectroactive materials (e.g., electroactive anode materials), betweenfirst and second current collectors, between first and second releaselayers, interspersed in first and/or second release layers, interspersedin a single release layer, or combinations thereof.

Further description of adhesion promoters are described in more detailbelow.

Although FIG. 7B shows a single layer 227 formed by the joining of tworelease layers 224A and 224B of FIG. 7A, it should be understood thatother configurations are also possible. For instance, in some casesrelease layers 224A and 224B are formed of different materials so thatthe joining of the two release layers results in two differentintermediate layers. In yet other embodiments, only one component of anelectrochemical cell to be joined includes a release layer, but a secondcomponent to be joined does not include a release layer. For example,electrode portion 212A of FIG. 7A may include release layer 224A, but asecond electrode portion to be joined with electrode portion 212A doesnot include a release layer. In some such embodiments, release layer224A may also have sufficient adhesive characteristics that allow it tobe joined directly to a component the second electrode. Such a releaselayer may be designed to not only have a high adhesive affinity to asurface of the first electrode portion (e.g., current collector 226A)and a relatively low adhesive affinity to a carrier substrate on whichthe first electrode portion was fabricated, but also a relatively highadhesive affinity to a surface of the second electrode portion. In otherembodiments, an adhesion promoter that has a high adhesive affinity toboth the release layer and the second electrode portion can be used.

In some embodiments, an electrode assembly including laminatedback-to-back electrode portions (e.g., at least two electroactive layersseparated by at least a current collector and optionally othercomponents), includes a release layer having a relatively low overallthickness. The release layer in this configuration may be a single layeror a combined layer (e.g., two layers adhered together using an adhesionpromoter) formed from the same or different materials as describedherein (e.g., layer 27 of FIG. 2B). The total thickness of the releaselayer in this configuration may be, for example, between 1-10 micronsthick, between 1-7 microns thick, between 1-6 microns thick, between 1-5microns thick, or between 1-3 microns thick. In certain embodiments, thethickness of the release layer in this configuration is about 10 micronsor less, about 6 microns or less, about 7 microns or less, about 5microns or less, or about 3 microns or less.

In another embodiment, two components of an electrochemical cell such aselectrode portions 212A and 212B are joined after removal of bothrelease layers 224A and 224B. For example, during fabrication of theelectrode, the release layer may be released along with the carriersubstrate, leaving behind only current collector 226, base electrodematerial layer 228, and optionally additional layers adjacent the baseelectrode material layer. Such an electrode portion can be joined withanother electrode portion and/or another component of theelectrochemical cell by applying an adhesion promoter such as anadhesive to one or more surfaces to be joined. In other embodiments, thetwo electrode layers are not joined by any adhesion promoter (e.g.,adhesive) or any release layer, but are simply laid against one another,e.g., in a “rolled” configuration, as described herein. Advantageously,in such and other embodiments (e.g., as shown in FIG. 7B), a support forthe current collector and base electrode material layer(s) is not neededand the electrochemical cell is self-supporting. This configuration canreduce the weight of the electrochemical cell, thereby increasing thecell's energy density.

In certain embodiments a release layer used to form a component of anelectrochemical cell is designed to withstand the application of a forceapplied to the component during fabrication and/or during cycling of thecell. For example, a release layer described herein may be compatiblewith the methods and articles described below relating to theapplication of force to electrochemical cells described herein.

As described herein, the adhesion promoter may include a formulationthat can solvate, dissolve portions of, and/or activate a surface of arelease layer to which the adhesion promoter formulation comes incontact to promote adhesion between the release layer and anothercomponent of the cell. In some embodiments, the adhesion promoter isrelatively inert with respect to other components of the cell (e.g.,current collector, electroactive material, electrolyte). In certainembodiments, the adhesion promoter may be formulated or applied (e.g.,in a certain amount or by a particular method) such that penetration ofthe adhesion promoter through the release layer is minimized so that theadhesion promoter does not react with one or more components of thecell. The particular adhesion promoter formulation may be designed suchthat it can be easily applied to a component of the cell, e.g., bytechniques such as coating, spraying painting, and other methodsdescribed herein and known to those of ordinary skill in the art.

In some embodiments, an adhesion promoter (e.g., an adhesive or asolvent solution) may include one or more of the materials that can beused to form the release layer. Typically, the adhesion promoter has adifferent formulation than that of the release layer; however, in someembodiments, the formulations may be substantially similar.

The release layer and/or an adhesion promoter may be formed of orinclude in its composition, for example, a metal, a ceramic, a polymer,or a combination thereof. As such, the release layer and/or adhesionpromoter may be conductive, semi-conductive, or insulating.

In some embodiments, a release layer and/or an adhesion promotercomprises a polymeric material. In some cases, at least a portion of thepolymeric material of the release layer and/or an adhesion promoter iscrosslinked; in other cases, the polymeric material(s) is substantiallyuncrosslinked. When included in an adhesion promoter formulation, apolymer may act as an adhesive to promote adhesion between twocomponents of an electrochemical cell.

Examples of polymeric materials are described herein.

In some cases, a release layer and/or an adhesion promoter comprisesless than 30% by weight of a crosslinked polymeric material (e.g., asdetermined after the primer layer has been dried). That is, less than30% by weight of the individual polymer chains which form the polymericmaterial of a particular layer may be crosslinked at at least oneintermediate (e.g., non-terminal) position along the chain with anotherindividual polymer chain within that layer. A release layer and/or anadhesion promoter may include, for example, less than 25% by weight,less than 20% by weight, less than 15% by weight, less than 10% byweight, less than 5% by weight, or less than 2% by weight, or 0% of acrosslinked polymeric material. In certain embodiments, a release layerand/or an adhesion promoter includes less than 30% by weight of acovalently crosslinked polymeric material. For example, a release layerand/or an adhesion promoter may include less than 25% by weight, lessthan 20% by weight, less than 15% by weight, less than 10% by weight,less than 5% by weight, or less than 2% by weight, or 0% of a covalentlycrosslinked polymeric material. In one particular embodiment, a releaselayer and/or an adhesion promoter is essentially free of covalentlycrosslinked material.

Sometimes, a release layer has a different degree of crosslinking withinthe layer. For instance, a first surface of a release layer may includea lesser amount of a crosslinked polymer, and a second surface of therelease layer may include higher amounts of crosslinked polymer. Theamount of crosslinking may be in the form a gradient within the layer.Other arrangements are also possible.

It should be understood that while a release layer and/or an adhesionpromoter may include a certain percentage of crosslinked polymericmaterial (e.g., less than 30% by weight of a crosslinked polymericmaterial), the total amount of polymeric material (e.g., combinedcrosslinked and non-crosslinked polymeric material) in the release layerand/or an adhesion promoter may vary, e.g., from 20-100% by weight ofthe release layer and/or an adhesion promoter (e.g., from 30-90 wt %,from 50-95 wt %, or from 70-100 wt %). The remaining material used toform the release layer and/or an adhesion promoter may include, forexample, a filler (e.g., conductive, semi-conductive, or insulatingfiller), a crosslinking agent, a surfactant, one or more solvents, othermaterials as described herein, and combinations thereof.

In certain embodiments, a release layer and/or an adhesion promoterincludes a UV curable material. For instance, at least 30 wt %, at least50 wt %, or at least 80 wt % of a release layer or a layer formed by anadhesion promoter may be a UV curable material. In other instances, atleast 30 wt %, at least 50 wt %, or at least 80 wt % of a release layeror a layer formed by an adhesion promoter is a non-UV curable material.In one embodiment, substantially all of a release layer and/or a layerformed by an adhesion promoter is non-UV curable.

In some embodiments, a release layer and/or an adhesion promoterdescribed herein comprises a material including pendant hydroxylfunctional groups. Hydroxyl groups may provide the release layer with arelatively high adhesive affinity to a first layer but a relativelymoderate or poor adhesive affinity to a second layer, or may allow anadhesion promoter to facilitate adhesion between a release layer andanother component (e.g., between two release layers). Non-limitingexamples of hydroxyl-containing polymers include poly vinyl alcohol(PVOH), polyvinyl butyral, polyvinyl formal, vinyl acetate-vinyl alcoholcopolymers, ethylene-vinyl alcohol copolymers, and vinyl alcohol-methylmethacrylate copolymers. The hydroxyl-containing polymer may havevarying levels of hydrolysis (thereby including varying amounts ofhydroxyl groups). For instance, a polymer (e.g., a vinyl-based polymer)may be greater than 50% hydrolyzed, greater than 60% hydrolyzed, greaterthan 70% hydrolyzed, greater than 80% hydrolyzed, greater than 90%hydrolyzed, greater than 95% hydrolyzed, or greater than 99% hydrolyzed.A greater degree of hydrolysis may allow, for example, better adhesionof the hydroxyl-containing material to certain materials and, in somecases, may cause the polymer to be less soluble in the electrolyte. Inother embodiments, a polymer having hydroxyl groups may be less than 50%hydrolyzed, less than 40% hydrolyzed, less than 30% hydrolyzed, lessthan 20% hydrolyzed, or less than 10% hydrolyzed with hydroxylfunctional groups. In some cases, a release layer and/or an adhesionpromoter is water soluble.

In some embodiments, a release layer and/or an adhesion promoterdescribed herein comprises polyvinyl alcohol. The polyvinyl alcohol in arelease layer and/or an adhesion promoter may be crosslinked in someinstances, and substantially uncrosslinked in other instances. In oneparticular embodiment, a release layer immediately adjacent a carriersubstrate comprises polyvinyl alcohol. In another embodiment, therelease layer consists essentially of polyvinyl alcohol. The polyvinylalcohol in such and other embodiments may be substantiallyuncrosslinked, or in other cases, less than 30% of the material used toform the first release layer is crosslinked. For instance, a releaselayer immediately adjacent a carrier substrate and including polyvinylalcohol may comprise less than 30% by weight, less than 20% by weight,less than 15% by weight, less than 10% by weight, less than 5% byweight, or less than 2% by weight, of crosslinked polyvinyl alcohol.Such a release layer may optionally be adjacent a second release layer,which may have a different material composition than that of the firstrelease layer.

The molecular weight of a polymer may also affect adhesive affinity andcan vary in a release layer and/or in an adhesion promoter. For example,the molecular weight of a polymer used in a release layer and/or anadhesion promoter may be between 1,000 g/mol and 5,000 g/mol, 5,000g/mol and 10,000 g/mol, between 10,000 g/mol and 15,000 g/mol, between,15,000 g/mol and 20,000 g/mol, between 20,000 g/mol and 30,000 g/mol,between 30,000 g/mol and 50,000 g/mol, between 50,000 g/mol and 100,000g/mol, or between 100,000 g/mol and 200,000 g/mol. Other molecularweight ranges are also possible. In some embodiments, the molecularweight of a polymer used in a release layer and/or an adhesion promotermay be greater than about 1,000 g/mol, greater than about 5,000 g/mol,greater than about 10,000 g/mol, greater than about 15,000 g/mol,greater than about 20,000 g/mol, greater than about 25,000 g/mol,greater than about 30,000 g/mol, greater than about 50,000 g/mol,greater than about 100,000 g/mol or greater than about 150,000 g/mol. Inother embodiments, the molecular weight of a polymer used in a releaselayer and/or an adhesion promoter may be less than about 150,000 g/mol,less than about 100,000 g/mol, less than about 50,000 g/mol, less thanabout 30,000 g/mol, less than about 25,000 g/mol, less than about 20,000g/mol, less than less than about 10,000 g/mol, about 5,000 g/mol, orless than about 1,000 g/mol.

In other embodiments, a release layer and/or an adhesion promotercomprises a conductive material such as a metal or a conductive polymer.For example, if the release layer also acts as a current collector afterbeing incorporated into the electrochemical cell, the release layer maybe formed of a material suitable for use as a current collector, asdescribed in more detail below.

A release layer and/or an adhesion promoter may include one or moresolvents, e.g., in its initial formulation when being applied to acomponent of an electrochemical cell. The particular solvent or solventcombination used may depend on, for example, the type and amounts of anyother materials in the formulation, the method of applying theformulation to the cell component, the inertness of the solvent withrespect to other components of the electrochemical cell (e.g., currentcollector, electroactive material, electrolyte). For example, aparticular solvent or solvent combination may be chosen based in part onit's ability to solvate or dissolve any other materials (e.g., apolymer, filler, etc.) in the formulation. For adhesion promoterformulations, the particular solvent or solvent combination may bechosen based in part on it's ability to solvate or dissolve portions ofa release layer to which the adhesion promoter formulation comes incontact, and/or its ability to activate a surface of the release layerto promote adhesion. In some cases, one or more solvents used can wet(and activate) a surface of a release layer to promote adhesion, butdoes not penetrate across the release layer. A combination of such andother factors may be taken into consideration when choosing appropriatesolvents.

Non-limiting examples of suitable solvents may include aqueous liquids,non-aqueous liquids, and mixtures thereof. In some embodiments, solventsthat may be used for a release layer and/or a adhesion promoter include,for example, water, methanol, ethanol, isopropanol, propanol, butanol,tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene,acetonitrile, cyclohexane, and mixtures thereof can be used. Additionalexamples of non-aqueous liquid solvents include, but are not limited to,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, sulfoxides, aliphatic ethers, cyclicethers, glymes, polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Fluorinated derivatives of the foregoing are may also be used.Of course, other suitable solvents can also be used as needed.

In one set of embodiments involving the use of a solvent combination foran adhesion promoter, a first solvent of the solvent combination may beused to solvate, dissolve, and/or activate portions of a release layerto which the adhesion promoter formulation comes in contact, and asecond solvent may be used to dilute or decrease the viscosity of theadhesion promoter formulation. For example, in one particular set ofembodiments, an adhesion promoter, which may be used to facilitateadhesion between two release layers comprising a polymer includingpendant hydroxyl functional groups (e.g., PVOH), may include a firstsolvent that solvates, dissolves, or activates the pendant hydroxylfunctional groups to promote adhesion between the release layers. Thefirst solvent may be, for example, a sulfoxide or any other suitablesolvent that can dissolve, solvate, or activate a polymer includingpendant hydroxyl functional groups (e.g., PVOH). The adhesion promotermay further include a second solvent that is miscible with the firstsolvent. The second solvent may, for example, be used to dilute ordecrease the viscosity of the adhesion promoter formulation and/orincrease the vapor pressure of the adhesion promoter formulation.Additional solvents (e.g., third, fourth solvents) may also be includedin the solvent combination. As described herein, one or more of thesolvents of the solvent combination may be inert with respect to othercomponents of the cell (e.g., current collector, electroactive material,electrolyte).

A solvent combination including a first solvent that may be used tosolvate, dissolve, and/or activate portions of a release layer to whichthe adhesion promoter formulation comes in contact, and at least asecond solvent (such as one having the properties described above), mayinclude an amount of the first solvent of greater than about 1 wt %,greater than about 5 wt %, greater than about 10 wt %, greater thanabout 20 wt %, greater than about 30 wt %, greater than about 40 wt %,greater than about 50 wt %, greater than about 60 wt %, greater thanabout 70 wt %, greater than about 80 wt %, or greater than about 90 wt %with respect to the total solvent combination. In other embodiments, thefirst solvent is present at an amount of less than about 90 wt %, lessthan about 80 wt %, less than about 70 wt %, less than about 60 wt %,less than about 50 wt %, less than about 40 wt %, less than about 30 wt%, less than about 20 wt %, less than about 10 wt %, less than about 5wt %, less than about 3 wt %, or less than about 1 wt % with respect tothe total solvent combination.

As described herein, an adhesion promoter may include in its formulationone or more solvents that can be used to facilitate adhesion between twocomponents (e.g., release layers) of an electrochemical cell. In somecases, the adhesion promoter includes in its formulation a solvent orsolvent combination without any polymer. In other embodiments, theadhesion promoter includes in its formulation a solvent or solventcombination along with a polymer, such as those described herein, thatmay act as an adhesive. The amount of polymer in the adhesion promoterformulation that is applied to a component of an electrochemical cellmay be, for example, less than or equal to about 20 wt %, less than orequal to about 15 wt %, less than or equal to about 10 wt %, less thanor equal to about 7 wt %, less than or equal to about 5 wt %, less thanor equal to about 4 wt %, less than or equal to about 3 wt %, less thanor equal to about 2 wt %, less than or equal to about 1 wt %, less thanor equal to about 0.5%, or less than or equal to about 0.1% with respectto the total weight of the adhesion promoter formulation.

The use of a polymer in an adhesion promoter formulation may, in someinstances, decrease the time required to promote adhesion betweencomponents of the cell compared to using a similar adhesion promoterformulation but without the polymer, all other conditions being equal.For instance, adhesion using an adhesion promoter that includes apolymer may take place at least 2 times, 3 times, 4 times, 5 times, or10 times faster than adhesion using an adhesion promoter that does notincludes the polymer. The use of an adhesion promoter formulationwithout a polymer, however, may simplify the adhesion process.

The thickness of a release layer and/or a layer formed by an adhesionpromoter (if a layer is formed at all) may vary over a range ofthicknesses. Typically, the thickness of a release layer is greater thanthe thickness of a layer formed by an adhesion promoter. The thicknessof a release layer may vary, for example, from about 0.1 microns toabout 50 microns, and the thickness of a layer formed by an adhesionpromoter may vary, for example, from about 0.001 microns to about 50microns. In some cases, an adhesion promoter is applied but does notresult in the formation of a layer having any appreciable thickness.

In some embodiments, the thickness of the release layer and/or adhesionpromoter layer may be between 0.001-1 microns thick, between 0.001-3microns thick, between 0.01-3 microns thick, between 0.01-5 micronsthick, between 0.1-1 microns thick, between 0.1 and 2 microns thick,between 0.1 and 3 microns thick, between 1-5 microns thick, between 5-10microns thick, between 5-20 microns thick, or between 10-50 micronsthick. In certain embodiments, the thickness of a release layer and/or alayer formed by an adhesion promoter is, e.g., about 10 microns or less,about 7 microns or less, about 5 microns or less, about 3 microns orless, about 2.5 microns or less, about 2 microns or less, about 1.5microns or less, about 1 micron or less, or about 0.5 microns or less.As noted above, a relatively thicker release layer may be suitable forapplications where the release layer is not incorporated into anelectrochemical cell (e.g., it is released along with a carriersubstrate), and a relatively thinner release layer may be desirablewhere the release layer is incorporated into the electrochemical cell.

Additional arrangements, components, and advantages of release layersare described in more detail in Provisional Patent Apl. Ser. No.61/236,322, filed Aug. 24, 2009, entitled “Release System forElectrochemical Cells”, which is incorporated herein by reference in itsentirety.

In some embodiments, a primer is used to facilitate electricalconduction and/or provide adhesive connection between a base electrodematerial layer (e.g., as part of an anode or a cathode) and a currentcollector. For example, primer layer 65 of FIG. 1 may facilitateadhesion between base electrode material layer 55 (e.g., comprising anelectroactive material such as sulfur) and current collector 60 ofcathode 50.

In some embodiments, primer arrangements described herein include firstand second primer layers, which can be of the same or differentmaterial. The first primer layer may be designed to provide goodadhesion to a conductive support (e.g., a current collector) and maycomprise, for example, a crosslinked or substantially uncrosslinkedpolymer (e.g., a binder) having hydroxyl functional groups, e.g.,polyvinyl alcohol. The materials used to form the second primer layermay be chosen such that the second primer layer adheres well to both thefirst primer layer and an electroactive layer. In certain embodimentsincluding combinations of first and second primer layers, one or both ofthe first and second primer layers comprises less than 30% by weight ofa crosslinked polymeric material. In other embodiments, one or both ofthe first and second primer layers comprises between 30-60% by weight ofa crosslinked polymeric material. A primer including only a single layerof polymeric material is also described.

In certain embodiments, the primer layers described herein areconstructed and arranged to have one or more of the following features:good adhesion and electrical conduction between the current collectorand the primer layer (e.g., a first primer layer), good adhesion andelectrical conduction between the first primer layer and a second primerlayer in a multi-layer primer, good adhesion and electrical conductionbetween the primer layer (e.g., a second primer layer) and a baseelectrode material layer (which may comprise electroactive materials andother optional additives such as electronically conductive materials),and prevention of possible corrosive effects of the base electrodematerial layer on the current collector, e.g., during charge and/ordischarge. Additionally, batteries described herein comprising primersdescribed herein may have lower area specific resistance than batteriesincluding certain commercial primers.

Primer layer(s) described herein are preferably thin (e.g., less thanabout 10 microns) to reduce overall battery weight. Furthermore, primerlayer(s) should be stable in the electrolyte and should not interferewith the structural integrity of the electrodes in order for theelectrochemical cell to have a high electrochemical “capacity” or energystorage capability (i.e., reduced capacity fade).

As described herein, a primer arrangement may include at least a firstand a second primer layer. One or both of the first primer layer andsecond primer layer may be formed of a polymeric material. The polymericmaterials used to form the two layers may be the same or different. Insome cases, at least a portion of the polymeric material of the firstand/or second primer layers is/are crosslinked; in other cases, thepolymeric material(s) is/are substantially uncrosslinked.

In some cases, the first and/or second primer layer comprises less thanor equal to 40% by weight, or less than or equal to 30% by weight of acrosslinked polymeric material (e.g., as determined after the primerlayer has been dried). That is, ess than or equal to 40% by weight, orless than or equal to 30% by weight of the individual polymer chainswhich form the polymeric material of a particular layer may becrosslinked at at least one intermediate (e.g., non-terminal) positionalong the chain with another individual polymer chain within that layer.One or both of the first and second primer layers may comprise less thanor equal to 25% by weight, less than or equal to 20% by weight, lessthan or equal to 15% by weight, less than or equal to 10% by weight,less than or equal to 5% by weight, less than or equal to 2% by weight,or 0% of a crosslinked polymeric material. In certain embodiments, thefirst and/or second primer layer comprises less than or equal to 40%, orless than or equal to 30% by weight of a covalently crosslinkedpolymeric material. For example, one or both of the first and secondprimer layers may comprise less than or equal to 25% by weight, lessthan or equal to 20% by weight, less than or equal to 15% by weight,less than or equal to 10% by weight, less than or equal to 5% by weight,less than or equal to 2% by weight, or 0% of a covalently crosslinkedpolymeric material. In one particular embodiment, one or both of thefirst and second primer layers is essentially free of covalentlycrosslinked material.

It should be understood that while a primer layer may include, forexample, less than or equal to 40%, or less than or equal to 30% byweight of a crosslinked polymeric material, the total amount ofpolymeric material (e.g., combined crosslinked and non-crosslinkedpolymeric material) in the primer layer may vary, e.g., from 20-90% byweight of the primer layer, as described in more detail below.

In one particular embodiment, a first primer layer comprises less than30% by weight of a crosslinked polymeric material (e.g., polyvinylalcohol) and a second primer layer also includes less than 30% by weightof a crosslinked polymeric material (e.g., polyacrylate, polyvinylpyrrolidone vinyl acetate copolymer, and polyvinyl butyral). In otherembodiments, one of the first and second primer layers comprises lessthan 30% by weight of a crosslinked polymeric material, and the other ofthe first and second primer layers comprises greater than 30% by weightof a crosslinked polymeric material. In yet other embodiments, both ofthe first and second primer layers may include greater than 30% byweight of a crosslinked polymeric material.

Sometimes, an electrode includes first and second primer layers that areformed of the same material, but the first and second primer layers havedifferent degrees of crosslinking. For instance, the first primer layermay comprise substantially uncrosslinked polyvinyl alcohol, and thesecond primer layer may comprise crosslinked polyvinyl alcohol. Otherarrangements are also possible.

In some embodiments, a primer comprises first primer layer separatedfrom second primer layer by intermediate layer, wherein an electroactivematerial is in electrical communication with the second primer layer. Insome embodiments, intermediate layer is a third primer layer.Accordingly, in some embodiments, primers including more than two primerlayers may be used as appropriate. In other embodiments, intermediatelayer is a conductive support material (e.g., a current collector), ametal layer, a plasma treated layer, an ionic layer, or the like. Thecomposition and thickness of the intermediate layer may be chosen, forexample, based on its electrical conductivity, adhesiveness, and/orother mechanical or physical properties. In other embodiments, anintermediate layer is positioned between an electroactive material and asecond primer layer, and/or between a first primer layer and aconductive support. In some cases, an electrode includes two or moreintermediate layers positioned between various layers of the electrode.

In some embodiments, a primer layer described herein (e.g., as part of amulti-layered primer assembly or a single-layer primer) compriseshydroxyl functional groups. Hydroxyl groups may provide good adhesion toa conductive support such as an aluminum foil and/or an aluminizedpolyethylene terephthalate (PET) film. Non-limiting examples ofhydroxyl-containing polymers include polyvinyl alcohol, polyvinylbutyral, polyvinyl formal, vinyl acetate-vinyl alcohol copolymers,ethylene-vinyl alcohol copolymers, and vinyl alcohol-methyl methacrylatecopolymers. The hydroxyl-containing polymer may have varying levels ofhydrolysis (thereby including varying amounts of hydroxyl groups). Forinstance, a vinyl-based polymer may be greater than 50% hydrolyzed,greater than 60% hydrolyzed, greater than 70% hydrolyzed, greater than80% hydrolyzed, greater than 90% hydrolyzed, greater than 95%hydrolyzed, or greater than 99% hydrolyzed. A greater degree ofhydrolysis may allow better adhesion of the hydroxyl-containing materialto a conductive support and, in some cases, may cause the polymer to beless soluble in the electrolyte. In other embodiments, a polymer havinghydroxyl groups may be less than 50% hydrolyzed, less than 40%hydrolyzed, less than 30% hydrolyzed, less than 20% hydrolyzed, or lessthan 10% hydrolyzed with hydroxyl functional groups. In one particularembodiment, a first primer layer comprises hydroxyl groups and a secondprimer layer has a different material composition than that of the firstprimer layer.

In some embodiments, a primer layer described herein comprises polyvinylalcohol. The polyvinyl alcohol in a primer layer may be crosslinked insome instances, and substantially uncrosslinked in other instances. Inone particular embodiment, a primer layer immediately adjacent aconductive support (e.g., a first primer layer) comprises polyvinylalcohol. In another embodiment, the primer layer consists essentially ofpolyvinyl alcohol. The polyvinyl alcohol in such embodiments may besubstantially uncrosslinked, or in other cases, less than 30% of thematerial used to form the first primer layer is crosslinked. Forinstance, a primer layer immediately adjacent a conductive support andincluding polyvinyl alcohol may comprise less than 30% by weight, lessthan 20% by weight, less than 15% by weight, less than 10% by weight,less than 5% by weight, or less than 2% by weight, of crosslinkedpolyvinyl alcohol. Such a primer layer may optionally be adjacent asecond primer layer, which may have a different material compositionthan that of the first primer layer. In some instances, the secondprimer layer is crosslinked. The second primer layer may comprise anysuitable material that can adhere well to the first primer layer and theelectroactive material. Examples of such materials include, but are notlimited to, polyvinyl butyral, polyacrylate, polyvinyl pyrrolidone, andpolyvinyl acetate, as well as copolymers thereof. Other suitablepolymers are described in more detail below. In one particularembodiment, the material used to form the second primer layer iscrosslinked so as to provide good adhesion between the first primerlayer and a sulfur-containing cathodes.

In certain embodiments, two primer layers of a primer comprise polymershaving hydroxyl functional groups. The percentage of hydroxyl functionalgroups in the polymers of the first and second primer layers may differ.For example, in one embodiment, the first primer layer comprises atleast at least 20% more, at least 40% more, at least 60% more, at least80% more, at least 100% more, at least 150% more, or at least 200% morehydroxyl groups than the second primer layer. One particular example isa first primer layer comprising polyvinyl alcohol and a second primerlayer comprising polyvinyl butyral (e.g., where polyvinyl alcohol hasbeen reacted to varying degrees with butanal and/or other compounds).

Primer layers can also include other polymeric materials, such as thosedescribed herein.

As mentioned above, a primer layer may include any suitable amount ofpolymeric material to achieve the desired properties. For example, thetotal amount of polymeric material (e.g., combined crosslinked andnon-crosslinked polymeric material) in a primer layer may be in therange of, for example, 20-90% by weight of the primer layer (e.g., asdetermined after drying the primer layer). In some instances, a primerlayer includes a total amount of a polymeric material in the range of,for example, 20-40%, 30-60%, 40-80%, or 60-80% by weight of the primerlayer. The remaining material used to form the primer layer may includea conductive filler, a crosslinking agent, and/or other materials asdescribed herein.

The thickness of a primer layer (e.g., a first and/or a second primerlayer) may vary over a range from about 0.1 microns to about 10 microns.For instance, the thickness of the primer layer may be between 0.1-1microns thick, between 1-5 microns thick, or between 5-10 microns thick.The thickness of a primer layer may be no greater than, e.g., 10 micronsthick, no greater than 7 microns thick, no greater than 5 microns thick,no greater than 3 microns thick, no greater than 2.5 microns thick, nogreater than 1 micron thick, no greater than 0.5 microns thick, nogreater than 0.3 microns thick, or no greater than 0.1 microns thick. Insome embodiments including a multi-layer primer, a first primer layerhas the same thickness as a second primer layer. In other embodiments,the first primer layer may have a different thickness than the secondprimer layer.

Additional arrangements, components, and advantages of primer layers aredescribed in more detail in International Patent Apl. Serial No.:PCT/US2008/012042, filed Oct. 23, 2008, entitled “Primer for BatteryElectrode”, which is incorporated herein by reference in its entirety.

An electrochemical cell may include any suitable current collector. Insome instances, the current collector is positioned immediately adjacenta release layer (e.g., on top of a release layer that has beenpositioned on a carrier substrate) and/or a primer layer, as describedherein. The current collector may have good adhesion to a release layerand/or primer layer where the release layer and/or primer layer isdesigned to be a part of the final electrochemical cell. In otherembodiments, the current collector may have poor adhesion to a releaselayer where the release layer is designed to be released along with acarrier substrate.

A current collector is useful in efficiently collecting the electricalcurrent generated throughout an electrode and in providing an efficientsurface for attachment of the electrical contacts leading to theexternal circuit. A wide range of current collectors are known in theart. Suitable current collectors may include, for example, metal foils(e.g., aluminum foil), polymer films, metallized polymer films (e.g.,aluminized plastic films, such as aluminized polyester film),electrically conductive polymer films, polymer films having anelectrically conductive coating, electrically conductive polymer filmshaving an electrically conductive metal coating, and polymer filmshaving conductive particles dispersed therein.

In some embodiments, the current collector includes one or moreconductive metals such as aluminum, copper, chromium, stainless steeland nickel. For example, a current collector may include a copper metallayer. Optionally, another conductive metal layer, such as titanium maybe positioned on the copper layer. The titanium may promote adhesion ofthe copper layer to another material, such as an electroactive materiallayer. Other current collectors may include, for example, expandedmetals, metal mesh, metal grids, expanded metal grids, metal wool, wovencarbon fabric, woven carbon mesh, non-woven carbon mesh, and carbonfelt. Furthermore, a current collector may be electrochemicallyinactive. In other embodiments, however, a current collector maycomprise an electroactive material. For example, a current collector mayinclude a material which is used as an electroactive material layer(e.g., as an anode or a cathode such as those described herein).

A current collector may be positioned on a surface (e.g., a surface of arelease layer) by any suitable method such as lamination, sputtering,and vapor deposition. In some cases, a current collector is provided asa commercially available sheet that is laminated with one or moreelectrochemical cell components. In other cases, a current collector isformed during fabrication of the electrode by depositing a conductivematerial on a suitable surface. Side or edge current collectors, such ascurrent collector 180 shown in FIG. 5, may also be incorporated intoelectrochemical cells described herein.

A current collector may have any suitable thickness. For instance, thethickness of a current collector may be, for example, between 0.1 and0.5 microns thick, between 0.1 and 0.3 microns thick, between 0.1 and 2microns thick, between 1-5 microns thick, between 5-10 microns thick,between 5-20 microns thick, or between 10-50 microns thick. In certainembodiments, the thickness of a current collector is, e.g., about 20microns or less, about 12 microns or less, about 10 microns or less,about 7 microns or less, about 5 microns or less, about 3 microns orless, about 1 micron or less, about 0.5 micron or less, or about 0.3micron or less. In some embodiments, the use of a release layer duringfabrication of an electrode can allow the formation or use of a verythin current collector, which can reduce the overall weight of the cell,thereby increasing the cell's energy density.

The electrolytes used in electrochemical cells can function as a mediumfor the storage and transport of ions, and in the special case of solidelectrolytes and gel electrolytes, these materials may additionallyfunction as a separator between the anode and the cathode. Any suitableliquid, solid, or gel material capable of storing and transporting ionsbetween the anode and the cathode may be used. The electrolyte may beelectronically non-conductive to prevent short circuiting between theanode and the cathode. In one set of embodiments a non-aqueous-basedelectrolyte is used; in another set of embodiments, an aqueous-basedelectrolyte is used.

In some embodiments, an electrolyte may be present as a polymer layer 75and/or 80 (e.g., a gel or solid polymer layer) as shown illustrativelyin FIG. 1. In some cases, in addition to being able to function as amedium for the storage and trasport of ions, a polymer layer positionedbetween an anode and cathode can function to screen the anode (e.g., abase electrode layer of the anode) from any cathode roughness under anapplied force or pressure, keeping the anode surface smooth under forceor pressure, and stabilizing any multi-layered structures of the anode(e.g., ceramic polymer multi-layer) by keeping the multi-layer pressedbetween the base electrode layer and the smooth polymer layer. In somesuch embodiments, the polymer layer may be chosen to be compliant andhave a smooth surface.

The electrolyte can comprise one or more ionic electrolyte salts toprovide ionic conductivity and one or more liquid electrolyte solvents,gel polymer materials, or polymer materials. Suitable non-aqueouselectrolytes may include organic electrolytes comprising one or morematerials selected from the group consisting of liquid electrolytes, gelpolymer electrolytes, and solid polymer electrolytes. Examples ofnon-aqueous electrolytes for lithium batteries are described by Dornineyin Lithium Batteries, New Materials, Developments and Perspectives,Chapter 4, pp. 137-165, Elsevier, Amsterdam (1994). Examples of gelpolymer electrolytes and solid polymer electrolytes are described byAlamgir et al. in Lithium Batteries, New Materials, Developments andPerspectives, Chapter 3, pp. 93-136, Elsevier, Amsterdam (1994).

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, aliphatic ethers, acyclic ethers, cyclicethers, glymes, polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Examples of acyclic ethers that may be used include, but arenot limited to, diethyl ether, dipropyl ether, dibutyl ether,dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane,1,2-dimethoxypropane, and 1,3-dimethoxypropane. Examples of cyclicethers that may be used include, but are not limited to,tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, 1,4-dioxane,1,3-dioxolane, and trioxane. Examples of polyethers that may be usedinclude, but are not limited to, diethylene glycol dimethyl ether(diglyme), triethylene glycol dimethyl ether (triglyme), tetraethyleneglycol dimethyl ether (tetraglyme), higher glymes, ethylene glycoldivinylether, diethylene glycol divinylether, triethylene glycoldivinylether, dipropylene glycol dimethyl ether, and butylene glycolethers. Examples of sulfones that may be used include, but are notlimited to, sulfolane, 3-methyl sulfolane, and 3-sulfolene. Fluorinatedderivatives of the foregoing are also useful as liquid electrolytesolvents. Mixtures of the solvents described herein can also be used.

In some embodiments, specific liquid electrolyte solvents that may befavorable towards the anode as described in more detail below (e.g.,have relatively low reactivity towards lithium, good lithium ionconductivity, and/or relatively low polysulfide solubility) include, butare not limited to 1,1-dimethoxyethane (1,1-DME), 1,1-diethoxyethane,1,2-diethoxyethane, diethoxymethane, dibutyl ether, anisole ormethoxybenzene, veratrole or 1,2-dimethoxybenzene, 1,3-dimethoxybenzene,t-butoxyethoxyethane, 2,5-dimethoxytetrahydrofurane, cyclopentanoneethylene ketal, and combinations thereof. Specific liquid electrolytesolvents that may be favorable towards the cathode (e.g., haverelatively high polysulfide solubility, and/or can enable high ratecapability and/or high sulfur utilization) include, but are not limitedto dimethoxyethane (DME, 1,2-dimethoxyethane) or glyme, diglyme,triglyme, tetraglyme, polyglymes, sulfolane, 1,3-dioxolane (DOL),tetrahydrofurane (THF), acetonirile, and combinations thereof.

Specific mixtures of solvents include, but are not limited to1,3-dioxolane and dimethoxyethane, 1,3-dioxolane and diethyleneglycoldimethyl ether, 1,3-dioxolane and triethyleneglycol dimethyl ether, and1,3-dioxolane and sulfolane. The weight ratio of the two solvents in themixtures may vary from about 5 to 95 to 95 to 5. In some embodiments, asolvent mixture comprises dioxolanes (e.g., greater than 40% by weightof dioxolanes).

In some cases, aqueous solvents can be used as electrolytes for lithiumcells. Aqueous solvents can include water, which can contain othercomponents such as ionic salts. In some embodiments, the electrolyte caninclude species such as lithium hydroxide, or other species renderingthe electrolyte basic, so as to reduce the concentration of hydrogenions in the electrolyte.

Liquid electrolyte solvents can also be useful as plasticizers for gelpolymer electrolytes. Examples of useful gel polymer electrolytesinclude, but are not limited to, those comprising one or more polymersselected from the group consisting of polyethylene oxides, polypropyleneoxides, polyacrylonitriles, polysiloxanes, polyirnides,polyphosphazenes, polyethers, sulfonated polyimides, perfluorinatedmembranes (NAFION resins), polydivinyl polyethylene glycols,polyethylene glycol diacrylates, polyethylene glycol dimethacrylates,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing,and optionally, one or more plasticizers.

Examples of useful solid polymer electrolytes include, but are notlimited to, those comprising one or more polymers selected from thegroup consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming electrolytes, the electrolyte may furthercomprise one or more ionic electrolyte salts, also as known in the art,to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytesdescribed herein include, but are not limited to, LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂. Other electrolyte salts that may beuseful include lithium polysulfides (Li₂S_(x)), and lithium salts oforganic ionic polysulfides (LiS_(x)R)_(n), where x is an integer from 1to 20, n is an integer from 1 to 3, and R is an organic group, and thosedisclosed in U.S. Pat. No. 5,538,812 to Lee et al. A range ofconcentrations of the ionic lithium salts in the solvent may be usedsuch as from about 0.2 m to about 2.0 m (m is moles/kg of solvent). Insome embodiments, a concentration in the range between about 0.5 m toabout 1.5 m is used. The addition of ionic lithium salts to the solventis optional in that upon discharge of Li/S cells the lithium sulfides orpolysulfides formed typically provide ionic conductivity to theelectrolyte, which may make the addition of ionic lithium saltsunnecessary. Furthermore, if an ionic N—O additive such as an inorganicnitrate, organic nitrate, or inorganic nitrite is used, it may provideionic conductivity to the electrolyte in which case no additional ioniclithium electrolyte salts may be needed.

As described herein, additives that may reduce or prevent formation ofimpurities and/or depletion of electrochemically active materialsincluding electrodes and electrolyte materials, during charge/dischargeof the electrochemical cell, may be incorporated into electrochemicalcells described herein.

In some cases, an additive such as an organometallic compound may beincorporated into the electrolyte and may reduce or prevent interactionbetween at least two components or species of the cell to increase theefficiency and/or lifetime of the cell. Typically, electrochemical cells(e.g., rechargeable batteries) undergo a charge/discharge cycleinvolving deposition of metal (e.g., lithium metal) on the surface ofthe anode (e.g., a base electrode material) upon charging and reactionof the metal on the anode surface to form metal ions, upon discharging.The metal ions may diffuse from the anode surface into an electrolytematerial connecting the cathode with the anode. The efficiency anduniformity of such processes may affect cell performance. For example,lithium metal may interact with one or more species of the electrolyteto substantially irreversibly form lithium-containing impurities,resulting in undesired depletion of one or more active components of thecell (e.g., lithium, electrolyte solvents). The incorporation of certainadditives within the electrolyte of the cell have been found, inaccordance with certain embodiments described herein, to reduce suchinteractions and to improve the cycling lifetime and/or performance ofthe cell.

In some embodiments, additives such as organometallic additives mayreduce or prevent formation of impurities, i.e., lithium-containingimpurities, or other species that may be formed during charge-dischargecycling of the electrochemical cell. In some cases, formation of theimpurities (e.g., depletion products) may advantageously be reducedand/or prevented while the cell is in early stages of operation, forexample, when the cell has been charged and discharged less than fivetimes in its lifetime. Incorporation of such additives withinelectrochemical cells may reduce formation of impurities and/ordepletion of the electrodes, electrolyte, and/or other species presentwithin the cell, and may improve overall cell performance. In someembodiments, the cells, devices, and methods described herein mayexhibit improved performance including reduced capacity fade, improvedmorphology of electrodes (e.g., anode, cathode) upon cycling, reducedlithium corrosion with electrolyte components (e.g., polysulfides),reduced cell polarization, reduced depletion of electrolyte solvent,etc.

In some embodiments, the additive may be any suitable species, or saltthereof, capable of reducing or preventing the depletion of activematerials (e.g., electrodes, electrolyte) within a cell, for example, byreducing formation of lithium-containing impurities within the cell,which may be formed via reaction between lithium and an electrolytematerial. In some embodiments, the additive may be an organic ororganometallic compound, a polymer, salts thereof, or combinationsthereof. In some embodiments, the additive may be a neutral species. Insome embodiments, the additive may be a charged species. Additivesdescribed herein may also be soluble with respect to one or morecomponents of the cell (e.g., the electrolyte). In some cases, theadditive may be an electrochemically active species. For example, theadditive may be a lithium salt which may reduce or prevent depletion oflithium and/or the electrolyte, and may also serve as anelectrochemically active lithium salt.

The additive may be present within (e.g., added to) the electrochemicalcell in an amount sufficient to inhibit (e.g., reduce or prevent)formation of impurities and/or depletion of the active materials withinthe cell. “An amount sufficient to inhibit formation of impuritiesand/or depletion of the active materials within the cell,” in thiscontext, means that the additive is present in a large enough amount toaffect (e.g., reduce) formation of impurities and/or the depletion ofthe active materials, relative to an essentially identical cell lackingthe additive. For example, trace amounts of an additive may not besufficient to inhibit depletion of active materials in the cell. Thoseof ordinary skill in the art may determine whether an additive ispresent in an amount sufficient to affect depletion of active materialswithin an electrochemical device. For example, the additive may beincorporated within a component of an electrochemical cell, such as theelectrolyte, and the electrochemical cell may be monitored over a numberof charge/discharge cycles to observe any changes in the amount,thickness, or morphology of the electrodes or electrolyte, or anychanges in cell performance. Determination of the amount of change inthe active materials over a number of charge/discharge cycles maydetermine whether or not the additive is present in an amount sufficientto inhibit formation of impurities and/or depletion of the activematerials. In some cases, the additive may be added to theelectrochemical cell in an amount sufficient to inhibit formation ofimpurities and/or depletion of active materials in the cell by at least50%, 60%, 70%, 80%, 90%, or, in some cases, by 100%, as compared to anessentially identical cell over an essentially identical set ofcharge/discharge cycles, absent the additive.

Although not wishing to be bound by any theory, the inventors offer thefollowing discussion of the relationship between the presence of theadditive and performance characteristics observed. In typical lithiumanode batteries, after a few charge/discharge cycles of a battery,adverse changes can occur, such as formation of impurities and/ordepletion of active materials. This may be due to interaction oflithium, or a lithium-containing compound, with one or more species inthe electrolyte to substantially irreversibly form an impurity, such asa lithium-containing impurity. In some cases, formation of the impuritymay comprise interaction between lithium, or a lithium-containingcompound, and a solvent present within the electrochemical cell, toproduce the impurity. In some cases, lithium or a lithium-containingcompound may react with a solvent comprising at least onecarbon-heteroatom bond (e.g., C—O, C═O, C—S, C═S, C—N, C═N, etc.) toform the lithium-containing impurity. In some cases, a sulfur-containingmaterial (e.g., sulfur, carbon disulfide, polysulfides, etc.) mayinteract with a solvent to form the lithium-containing impurity such asan alkyl polysulfide, carbon disulfide, polythiocarbonate,polythiocarboxylate, or the like.

The presence of additives within a cell may reduce and/or substantiallyinhibit formation of impurities, thereby reducing active materialdepletion and improving the performance and/or lifetime of thebatteries. In some cases, the additive, incorporated within the cellfrom a source external to the cell, may have the same chemical structureas a compound (e.g., a depletion product) that may be formed as a resultof a substantially irreversible reaction between lithium of the anodewith one or more species present within the electrolyte, under normalcharge and/or discharge of the cell. However, the external additive maynot be the product of such a reaction. That is, the additive may havethe same chemical structure as a “depletion product” of the cell,although the additive is produced from and/or provided by a sourceexternal to the cell. In some cases, the additive may be incorporatedwithin an electrochemical cell prior to use of the cell. In some cases,the additive may be incorporated within an electrochemical cell havingbeen charged and discharged less than five times under set conditions.As used herein, “set conditions” may comprise, for example, applicationof a particular voltage, temperature, pKa, solvent, chemical reagent,type of atmosphere (e.g., nitrogen, argon, oxygen, etc.), or the like,for a particular period of time.

In some cases, the additive may have the same chemical structure as aproduct of a reaction between lithium of the anode and a solvent withinthe electrolyte, such as an ester, ether, acetal, ketal, or the like.Examples of such solvents include, but are not limited to,1,2-dimethoxyethane and 1,2-dioxolane.

In some cases, the additive may be an organometallic compound, includingsalts. In some cases, the additive is a lithium compound, such as alithium salt. The additive (e.g., the external additive) may have theformula LiR or (Li—X)_(n)R′, wherein R comprises a heteroalkyl orheteroaryl group, optionally substituted; R′ comprises an alkyl or arylgroup, optionally substituted; X may be a heteroatom; and n may be aninteger equal to or greater than 1. In some cases, R may be —O-alkyl,—O-aryl, —O-heteroaryl, —S-alkyl, —S-aryl, —S-heteroaryl, optionallysubstituted. In some cases, R may be —O-alkyl, —O— alkoxyalkyl,—S-alkyl, or —S-alkoxyalkyl. In some cases, R may comprise an alcohol ora carboxyl group. Examples of such additives include lithium2-methoxyethoxide or lithium methoxide. In one set of embodiments, theadditive is lithium methoxide.

In some cases, the additives described herein may be associated with apolymer. For example, the additives may be combined with a polymermolecule or may be bonded to a polymer molecule. In some cases, theadditive may be a polymer. For example, the additive may have theformula, R′—(O—Li)_(n), wherein R′ is alkyl or alkoxyalkyl.

As described above, some embodiments described herein relate to devicescomprising an electrochemical cell having been charged and dischargedless than five times under set conditions. The cell may comprise ananode comprising lithium, a cathode, and an electrolyte inelectrochemical communication with the anode. The electrolyte maycomprise a lithium compound additive, which, under normal charge and/ordischarge of the cell, can be produced through a substantiallyirreversible reaction between the lithium of the anode and at least oneother species of the cell during charge and/or discharge of the cell.However, in some cases, the lithium compound additive may be present inthe cell in an amount greater than that formed through charge anddischarge of the cell five times under the set conditions. That is, thelithium compound additive can be provided to the cell from a sourceexternal to the cell, in an amount greater than would be producedinternally within the cell through five charge and discharge cycles.

Advantageously, the additive may be present within an electrochemicalcell described herein in an amount sufficient to reduce or preventinternal formation of impurities during charge and/or discharge. Theadditive may be introduced into the cell prior to depletion of activematerial(s) and/or deterioration of cell performance. In some cases, theadditive is advantageously provided prior to use of the cell, or in theearly stages of use of the cell (e.g., when the cell has been chargedand discharged less than five times under set conditions). For example,the additive may have the same chemical formula as an impurity ordepletion product of the electrochemical cell, such that introduction ofthe additive in an amount sufficient to saturate the electrochemicalcell may reduce and/or prevent internal formation of the impurity. Thatis, the amount of electrolyte, lithium, depletion product, and/or otherspecies present within the cell may affect the equilibrium of a reactionwhich can generate a depletion product, such that addition of thedepletion product, in an amount sufficient to affect the equilibrium ofthe reaction (e.g., to drive the equilibrium in a direction whichreduces formation of the impurity), may reduce or prevent formation ofthe depletion product.

In some embodiments, an additive is added to an electrochemical cell,wherein the additive is an electrochemically active species. Forexample, the additive can serve as electrolyte salt and can facilitateone or more processes during charge and/or discharge of the cell. Insome cases, the additive may be substantially soluble or miscible withone or more components of the cell. In some cases, the additive may be asalt which is substantially soluble with respect to the electrolyte. Theadditive may serve to reduce or prevent formation of impurities withinthe cell and/or depletion of the active materials, as well as facilitatethe charge-discharge processes within the cell.

Incorporation of additives described herein may allow for the use ofsmaller amounts of lithium and/or electrolyte within an electrochemicalcell, relative to the amounts used in essentially identical cellslacking the additive. As described above, cells lacking the additivesdescribed herein may generate lithium-containing impurities and undergodepletion of active materials (e.g., lithium, electrolyte) duringcharge-discharge cycles of the cell. In some cases, the reaction whichgenerates the lithium-containing impurity may, after a number ofcharge-discharge cycles, stabilize and/or begin to self-inhibit suchthat substantially no additional active material becomes depleted andthe cell may function with the remaining active materials. For cellslacking additives as described herein, this “stabilization” is oftenreached only after a substantial amount of active material has beenconsumed and cell performance has deteriorated. Therefore, in somecases, a relatively large amount of lithium and/or electrolyte has oftenbeen incorporated within cells to accommodate for loss of materialduring consumption of active materials, in order to preserve cellperformance.

Accordingly, incorporation of additives as described herein may reduceand/or prevent depletion of active materials such that the inclusion oflarge amounts of lithium and/or electrolyte within the electrochemicalcell may not be necessary. For example, the additive may be incorporatedinto a cell prior to use of the cell, or in an early stage in thelifetime of the cell (e.g., less than five charge-discharge cycles),such that little or substantially no depletion of active material mayoccur upon charging or discharging of the cell. By reducing and/oreliminating the need accommodate for active material loss duringcharge-discharge of the cell, relatively small amounts of lithium may beused to fabricate cells and devices as described herein. In someembodiments, devices described herein comprise an electrochemical cellhaving been charged and discharged less than five times in its lifetime,wherein the cell comprises an anode comprising lithium, a cathode, andan electrolyte, wherein the anode comprises no more than five times theamount of lithium which can be ionized during one full discharge cycleof the cell. In some cases, the anode comprises no more than four,three, or two times the amount of lithium which can be ionized duringone full discharge cycle of the cell.

In some cases, devices described herein comprise an electrochemical cellhaving been charged and discharged less than five times in its lifetime,wherein the cell comprises an anode comprising lithium (e.g., lithiummetal), a cathode active material (e.g., sulfur), and an electrolyte,wherein the molar ratio of cathode active material to lithium (e.g.,lithium metal) may be at least 0.1. For example, a cell may comprisesulfur and lithium (e.g., lithium metal), wherein the molar ratio S:Li(e.g., lithium metal) is equal to or greater than 0.1. In some cases,the molar ratio of cathode active material to lithium is at least 0.3,at least 0.5, at least 0.7, or greater. In some embodiments, the ratioof cathode active material to lithium (e.g., lithium metal) by weightmay be at least 0.46. For example, a cell may comprise sulfur andlithium, wherein the ratio S:Li by weight is equal to or greater than0.46. In some cases, the ratio of cathode active material to lithium byweight is at least 0.5, at least 0.7, at least 0.9, or greater. In someembodiments, the ratio of cathode active material to electrolyte byweight is at least 0.17. In some cases, the ratio of cathode activematerial to lithium by weight is at least 0.2, at least 0.5, at least0.7, or greater. In some embodiments, the cathode active material is asulfur-containing material (e.g., elemental sulfur). Other examples ofcathode active materials are described more fully herein.

The use of smaller amounts of lithium and/or electrolyte materials mayadvantageously allow for electrochemical cells, or portions thereof,having decreased thickness. In some embodiments, devices describedherein comprise an electrochemical cell having been charged anddischarged less than five times in its lifetime, wherein the cellcomprises an anode comprising lithium, a cathode, and an electrolytelayer, and wherein the anode layer and the electrolyte layer togetherhave a maximum thickness of 500 microns. In some cases, the anode layerand the electrolyte layer together have a maximum thickness of 400microns, 300 microns, 200 microns, or, in some cases, 100 microns.

It may be advantageous, in some cases, for an electrochemical cell ordevice to have the ability to react a large amount of lithium metal upondischarge in a reaction that is substantially reversible during normalcell charge and/or discharge, i.e., the cell or device may have a large“depth of discharge.” In some embodiments, such substantially reversiblyreactions do not include, for example, consumption of lithium metal in asubstantially irreversible reaction to form an impurity. In some cases,electrochemical cells, devices, and methods comprising an additive asdescribed herein may have the ability to react a greater amount oflithium metal upon discharge in a substantially reversible reaction,relative to essentially identical cells, devices, and methods lackingthe additive, with little or essentially no deterioration of cellperformance due to, for example, morphological changes at the electrode.

In some embodiments, in an electrochemical cell having been charged anddischarged less than five times in its lifetime, at least 20% of thelithium from the anode is reacted upon discharge in a reaction that issubstantially reversible during normal cell charge and/or discharge. Insome cases, at least 30%, 50%, 70%, or, in some cases, at least 90%, ofthe lithium from the anode is reacted upon discharge in a reaction thatis substantially reversible during normal cell charge and/or discharge.In some cases, essentially 100% of the lithium from the anode is reactedupon discharge in a reaction that is substantially reversible duringnormal cell charge and/or discharge. For example, for a particularnumber of charge-discharge cycles, an essentially identical amount oflithium metal may be depleted from the anode in each discharge cycle,and plated at the anode in each charge cycle.

In some embodiments, when an additive is added into the electrolyte thatis added to the electrochemical cell during fabrication, the additivemay first be introduced into the cell as a part of other cell componentsfrom where it can enter the electrolyte. The additive may beincorporated into liquid, gel or solid polymer electrolytes. In someembodiments, the additive may be incorporated in the cathode formulationor into the separator in the fabrication process, as long as it isincluded in a manner such that it will enter the electrolyte insufficient concentrations. Thus during discharge and charge of the cell,the additive incorporated in the cathode formulation or the separatormay dissolve in the electrolyte.

In some embodiments, an N—O compound can be used as an additive. N—Ocompounds for use as additives include, but are not limited to, familiessuch as inorganic nitrates, organic nitrates, inorganic nitrites,organic nitrites, organic nitro compounds, compounds with negatively,neutral and positively charged NO_(x) groups, and other organic N—Ocompounds. Examples of inorganic nitrates that may be used include, butare not limited to, lithium nitrate, potassium nitrate, cesium nitrate,barium nitrate, and ammonium nitrate. Examples of organic nitrates thatmay be used include, but are not limited to, dialkyl imidazoliumnitrates, and guanidine nitrate. Examples of inorganic nitrites that maybe used include, but are not limited to, lithium nitrite, potassiumnitrite, cesium nitrite, and ammonium nitrite. Examples of organicnitrites that may be used include, but are not limited to, ethylnitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octylnitrite. Examples organic nitro compounds that may be used include, butare not limited to, nitromethane, nitropropane, nitrobutanes,nitrobenzene, dinitrobenzene, nitrotoluene, dinitrotoluene,nitropyridine, and dinitropyridine. Examples of other organic N—Ocompounds that may be used include, but are not limited to, pyridineN-oxide, alkylpyridine N-oxides, and tetramethyl piperidine N-oxyl(TEMPO). These and other additives, which may stabilizelithium/electrolyte reactivity, may increase rate of polysulfidedissolution and/or increase sulfur utilization, are described in moredetail in U.S. Pat. No. 7,553,590, entitled “Electrolytes for lithiumsulfur cells,” which is incorporated herein by reference in itsentirety.

Concentrations of the N—O additive in the electrolytes may be from about0.02 m to about 2.0 m (e.g., from about 0.1 m to about 1.5 m, or fromabout 0.2 m to about 1.0 m). Concentrations of the ionic N—O additivewhen used in embodiments that do not include added lithium salts mayvary from about 0.2 m to about 2.0 m.

In some embodiments, electrochemical cells described herein are adaptedand arranged such that electrolyte compositions are separated todifferent portions of the cell. Such separation can result in isolationof a particular species from a portion of the electrochemical cell, orat least reduction in level of exposure of that portion to the species,for a variety of purposes, including prevention of deposition of certainsolids on or within electrodes of devices of this type.

Separation of electrolyte compositions described herein can be carriedout in a variety of manners. In one set of techniques, a polymer (whichcan be a gel) is positioned at a location in the device where it isdesirable for a particular electrolyte solvent, which has relativelyhigh affinity for the polymer, to reside. In another set of techniques,two different polymers are positioned in the device at particularlocations where two different electrolyte solvents, each having arelatively greater affinity for one of the polymers, are desirablypositioned. Similar arrangements can be constructed using more than twopolymers. Relatively immiscible electrolyte solvents can be used, andpositioned relative to each other, and to other components of thedevice, so as to control exposure of at least one component of thedevice to a particular species, by exploiting the fact that the speciesmay be more highly soluble in one solvent than the other. Techniquesdescribed generally above, or other techniques, or any combination, canbe used toward this general separation methodology.

As described herein, an electrochemical cell may include an anode havinglithium (e.g., lithium metal, a lithium intercalation compound, or alithium alloy) as the active anode species and a cathode having sulfuras the active cathode species. In these and other embodiments, suitableelectrolytes for the lithium batteries can comprise a heterogeneouselectrolyte including a first electrolyte solvent (e.g., dioxolane(DOL)) that partitions towards the anode and is favorable towards theanode (referred to herein as an “anode-side electrolyte solvent”) and asecond electrolyte solvent (e.g., 1,2-dimethoxyethane (DME)) thatpartitions towards the cathode and is favorable towards the cathode (andreferred to herein as an “cathode-side electrolyte solvent”). In someembodiments, the anode-side electrolyte solvent has a relatively lowerreactivity towards lithium metal and may be less soluble to polysulfides(e.g., Li₂S_(x), where x>2) than the cathode-side electrolyte solvent.The cathode-side electrolyte solvent may have a relatively highersolubility towards polysulfides, but may be more reactive towardslithium metal. By separating the electrolyte solvents during operationof the electrochemical cell such that the anode-side electrolyte solventis present disproportionately at the anode and the cathode-sideelectrolyte solvent is present disproportionately at the cathode, theelectrochemical cell can benefit from desirable characteristics of bothelectrolyte solvents (e.g., relatively low lithium reactivity of theanode-side electrolyte solvent and relatively high polysulfidesolubility of the cathode-side electrolyte solvent). Specifically, anodeconsumption can be decreased, buildup of insoluble polysulfides (i.e.,“slate”, lower-order polysulfides such as Li₂S_(x), where x<3, e.g.,Li₂S₂ and Li₂S) at the cathode can be decreased, and as a result, theelectrochemical cell may have a longer cycle life. Furthermore, thebatteries described herein may have a high specific energy (e.g.,greater than 400 Wh/kg), improved safety, and/or may be operable at awide range of temperatures (e.g., from −70° C. to +75° C.).Disproportionate presence of one species or solvent, verses another, ata particular location in a cell means that the first species or solventis present, at that location (e.g., at a surface of a cell electrode) inat least a 2:1 molar or weight ratio, or even a 5:1, 10:1, 50:1, or100:1 or greater ratio.

As used herein, a “heterogeneous electrolyte” is an electrolyteincluding at least two different liquid solvents (oftentimes referred toherein as first and second electrolyte solvents, or anode-side andcathode-side electrolyte solvents). The two different liquid solventsmay be miscible or immiscible with one another, although in many aspectsof the invention, electrolyte systems include one or more solvents thatare immiscible (or can be made immiscible within the cell) to the extentthat they will largely separate and at least one can be isolated from atleast one component of the cell. A heterogeneous electrolyte may be inthe form of a liquid, a gel, or a combination thereof. Specific examplesof heterogeneous electrolytes are provided below.

As certain embodiments described herein involve a heterogeneouselectrolyte having at least two electrolyte solvents that can partitionduring operation of the electrochemical cell, one goal may be to preventor decrease the likelihood of spontaneous solvent mixing, i.e.,generation of an emulsion of two immiscible liquids. As described inmore detail below, this may be achieved in some embodiments by“immobilizing” at least one electrolyte solvent at an electrode (e.g.,an anode) by forming, for example, a polymer gel electrolyte,glassy-state polymer, or a higher viscosity liquid that residesdisproportionately at that electrode.

In some embodiments, an anode includes a polymer layer adjacent amulti-layered structure of the anode (e.g., positioned as an outerlayer). The polymer layer can, in some instances, be in the form of apolymer gel or a glassy-state polymer. The polymer layer may have anaffinity to one electrolyte solvent of a heterogeneous electrolyte suchthat during operation of the electrochemical cell, a first electrolytesolvent resides disproportionately at the anode, while the a secondelectrolyte solvent is substantially excluded from the polymer layer andis present disproportionately at the cathode. For example, in theillustrative embodiment of FIG. 1, a first electrolyte solvent mayreside predominately at a polymer layer 75 adjacent the anode.

Because the first electrolyte solvent is present closer to the anode, itis generally chosen to have one or more characteristics such as lowreactivity to lithium (e.g., enable high lithium cycle-ability),reasonable lithium ion conductivity, and relatively lower polysulfidesolubility than the second electrolyte solvent (since polysulfides canreact with lithium). The second electrolyte solvent may be presentdisproportionately at the cathode and, for example, may residesubstantially in a separator, a polymer layer adjacent the cathode,and/or in a base electrode material layer of the cathode (e.g., cathodeactive material layer). For example, in the illustrative embodiment ofFIG. 1, a second electrolyte solvent may reside predominately at apolymer layer 80 adjacent the cathode, predominately in the baseelectrode material layer 55, or in combinations thereof. In someinstances, the second electrolyte solvent is essentially free of contactwith the anode. The second electrolyte solvent may have characteristicsthat favor better cathode performance such as high polysulfidesolubility, high rate capability, high sulfur utilization, and highlithium ion conductivity, and may have a wide liquid state temperaturerange. In some cases, the second electrolyte solvent has a higherreactivity to lithium than the first electrolyte solvent. It may bedesirable, therefore, to cause the second electrolyte solvent to bepresent at the cathode (i.e., away from the anode) during operation ofthe battery, thereby effectively reducing it's concentration, andreactivity, at the anode.

As described above, the first electrolyte solvent of a heterogeneouselectrolyte may be present disproportionately at the anode by residingin a polymer layer positioned adjacent a multi-layered structure.Accordingly, the material composition of the polymer layer may be chosensuch that the polymer has a relatively higher affinity to (highsolubility in) the first electrolyte solvent compared to the secondelectrolyte solvent. For instance, in some embodiments, the polymerlayer is prepared in the form of a gel by mixing a monomer, a firstelectrolyte solvent, and optionally other components (e.g., acrosslinking agent, lithium salts, etc.) and disposing this mixture onthe anode. The monomer can be polymerized by various methods (e.g.,using a radical initiator, ultra violet radiation, an electron beam, orcatalyst (e.g., an acid, base, or transition metal catalyst)) to form agel electrolyte. Polymerization may take place either before or afterdisposing the mixture on the anode. After assembling the othercomponents of the battery, the battery can be filled with the secondelectrolyte solvent. The second electrolyte solvent may be excluded fromthe polymer layer (e.g., due to the high affinity of the polymer withthe first electrolyte solvent already present in the polymer layerand/or due to immiscibility between the first and second electrolytesolvents). In some instances, the second electrolyte solvent may fillthe spaces (e.g., pores) within the separator and/or the cathode. Insome embodiments, the cathode can be dried prior to assembly of thebattery to facilitate this process. Additionally and/or alternatively,the cathode (e.g., base electrode material layer of the cathode) mayinclude a polymer that has a high affinity for the second electrolytesolvent. The polymer in the base electrode material layer may be in theform of particles. In some cases, the second electrolyte can reside atleast partially in a polymer layer positioned adjacent the cathode.

In another embodiment, a polymer layer is formed at the anode and isdried prior to assembly of the battery. The battery can then be filledwith a heterogeneous electrolyte including the first and secondelectrolyte solvents. If the polymer layer is chosen such that it has ahigher affinity towards the first electrolyte solvent (and/or theseparator and/or cathode may have a higher affinity towards the secondelectrolyte solvent), at least portions of the first and secondelectrolyte solvents can partition once they are introduced into thebattery. In yet another embodiment, partitioning of the first and secondelectrolyte solvents can take place after commencement of firstdischarge of the battery. For example, as heat is produced whileoperating the battery, the affinity between the polymer layer and thefirst electrolyte solvent can increase (and/or the affinity between theseparator and/or cathode and the second electrolyte solvent canincrease). Thus, a greater degree of partitioning of the electrolytesolvents can occur during operation of the battery. Additionally, atlower temperatures, the effect may be irreversible such that the firstelectrolyte solvent is trapped within the polymer layer, and the secondelectrolyte solvent is trapped within the pores of the separator and/orcathode. In some cases, the components of the battery (e.g., the polymerlayer) may be pretreated (e.g., with heat) prior to use to affect thedesired degree of polymer/electrolyte solvent interaction. Other methodsof partitioning the electrolyte solvents are also possible.

In another embodiment, the polymer layer is deposited at the anode andthe anode (including the polymer layer) is exposed to a firstelectrolyte solvent. This exposure can cause the first electrolytesolvent to be absorbed in the polymer. The battery can be formed bypositioning a cathode adjacent the anode such that the polymer layer ispositioned between the anode and cathode. The cathode can then beexposed to a second electrolyte solvent, e.g., such that at least aportion of the second electrolyte solvent is absorbed in the cathode. Inother embodiments, the cathode can be exposed to the second electrolytesolvent prior to assembly of the anode and cathode. Optionally, thecathode may include a polymer layer that preferentially absorbs thesecond electrolyte solvent more than the first electrolyte solvent. Insome embodiments, e.g., by choosing appropriate polymer(s) and/ormaterials used to form the anode and/or cathode, at least portions ofthe first and second electrolyte solvents can be separated within thebattery. For instance, a higher proportion of the first electrolytesolvent may reside at the anode and a higher proportion of the secondelectrolyte solvent may reside at the cathode.

In yet another embodiment, an electrochemical cell does not include apolymer layer specifically used for partitioning at the anode or thecathode. A separator may include a different composition near the anodeside compared to the cathode side of the separator, the anode sidehaving a higher affinity for the first solvent and the cathode sidehaving a higher affinity for the second solvent. Additionally and/oralternatively, the second electrolyte solvent may be presentdisproportionately at the cathode by, for example, fabricating thecathode such that it contains a component that has a high affinity forthe second electrolyte solvent.

In some of the embodiments described herein, a battery may be filledwith a heterogeneous electrolyte including first and second electrolytesolvents and partitioning of the electrolyte solvents can occur aftercommencement of first discharge of the battery, e.g., due to thedifferential solubility of the polysulfides in the electrolyte solvents.For example, as more polysulfides are generated during operation of thecell, the dissolution of the polysulfides in the more favorable secondelectrolyte solvent can cause it to become immiscible with the first.Thus, in some embodiments, the first and second electrolyte solvents maybe miscible before, but immiscible after, commencement of firstdischarge of the battery. The second electrolyte solvent containing thedissolved polysulfides may be present disproportionately at the cathodeby, for example, embodiments described herein such as having a polymerlayer at the anode that preferentially associates with the firstelectrolyte solvent, and/or a polymer layer at the cathode thatpreferentially associates with the second electrolyte solvent. In otherembodiments, the first and second electrolyte solvents are misciblebefore commencement of first discharge of the battery, but theelectrolyte solvents become immiscible due to heating of the electrolytesolvents during operation of the battery. In yet other embodiments, thefirst and second electrolyte solvents are immiscible before and aftercommencement of first discharge of the battery. For instance, the firstand second electrolyte solvents may be inherently immiscible at roomtemperature, as well as during operation of the battery. Advantageously,in some embodiments, two immiscible liquid electrolyte solvents, onepresent disproportionately and the anode and the other presentdisproportionately and the cathode, do not cause additional mechanicalstress to the battery as a solid membrane may, during electrode volumechanges that occur during cell cycling.

As described herein, in some embodiments a polymer that has an affinityfor an electrolyte solvent can be dispersed within the cathode (e.g., ina base electrode material layer). For instance, the cathode activematerial layer may include a polymeric material in powder formincorporated therein. In some cases, the polymeric material is aninsoluble component in the cathode layer. For example, the polymericmaterial may be insoluble in the solvent used to dissolve the cathodeactive material. The polymer can be obtained, or modified, to have asuitable particle size and dispersed throughout the cathode byincorporation in the cathode slurry. One advantage of incorporating aninsoluble polymer with the cathode active material layer is that thepolymer can remain as discrete particles that do not coat, adsorb,and/or block the active carbon sites. In other cases, however, thepolymeric material can be dissolved, or partially dissolved, as thecathode binder in the cathode layer.

In certain embodiments including one or more polymers dispersed within alayer (e.g., insoluble polymeric particles dispersed in a cathode), thepolymers can have any suitable particle size. The average diameter ofthe polymer particles may be, for example, less than or equal to 100microns, less than or equal to 70 microns, less than or equal to 50microns, less than or equal to 30 microns, less than or equal to 15microns, less than or equal to 10 microns, or less than or equal to 5microns. Of course, a range of polymer particle sizes may be used. Forexample, in one embodiment, the polymer particles may have a size ofd10=5, d50=12, and d97=55 microns, meaning 10% of the particles werebelow 5 microns, 50% of the particles below 12 microns, and only 3% ofthe particles measured above 55 microns.

Suitable polymer materials for partitioning electrolyte solvents mayinclude the polymers described herein, such as those mentioned aboveregarding suitable polymeric materials for polymer layers (e.g., as partof a multi-layer protective structure).

In some embodiments, a single polymer layer is in contact with an anodeor cathode of a battery; however, in other embodiments, more than onepolymer layer can be associated with an anode or cathode. For instance,a polymer layer in contact with an anode (or cathode) may be formed ofmore than one polymer layer coated in sequence. The sequence of polymersmay include, for example, a first polymer and a second polymer, thefirst and second polymers being the same or different. Additionalpolymers, e.g., fourth, fifth, or sixth polymer layers, can also beused. Each of the polymer layers may optionally include one or morefillers or other components (e.g., crosslinking agents, lithium salts,etc.).

The thickness of a polymer layer may vary, e.g., over a range from about0.1 microns to about 100 microns. The thickness of the polymer layer maydepend on, for example, whether it is positioned adjacent the anode orcathode, whether a separator is also present in the battery, and/or thenumber of polymer layers in the battery. For instance, the thickness ofthe polymer layer may be between 0.1-1 microns thick, between 1-5microns thick, between 5-10 microns thick, between 10-30 microns thick,or between 30-50 microns thick, between 50-70 microns thick, or between50-100 microns thick. In some embodiments, the thickness of a polymerlayer may be no greater than, e.g., 50 microns thick, no greater than 25microns thick, no greater than 10 microns thick, no greater than 5microns thick, no greater than 2.5 microns thick, no greater than 1micron thick, no greater than 0.5 microns thick, or no greater than 0.1microns thick.

In some embodiments, electrochemical cells may further comprise aseparator interposed between the cathode and anode. The separator may bea solid non-conductive or insulative material which separates orinsulates the anode and the cathode from each other preventing shortcircuiting, and which permits the transport of ions between the anodeand the cathode.

The pores of the separator may be partially or substantially filled withelectrolyte. Separators may be supplied as porous free standing filmswhich are interleaved with the anodes and the cathodes during thefabrication of cells. Alternatively, the porous separator layer may beapplied directly to the surface of one of the electrodes, for example,as described in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley et al.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes and polypropylenes,glass fiber filter papers, and ceramic materials. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree standing film or by a direct coating application on one of theelectrodes, as described in U.S. patent application Ser. Nos. 08/995,089and 09/215,112 by Carlson et al. of the common assignee. Solidelectrolytes and gel electrolytes may also function as a separator inaddition to their electrolyte function.

Suitable cathode active materials for use in the cathode of theelectrochemical cells described herein include, but are not limited to,electroactive transition metal chalcogenides, electroactive conductivepolymers, and electroactive sulfur-containing materials, andcombinations thereof. As used herein, the term “chalcogenides” pertainsto compounds that contain one or more of the elements of oxygen, sulfur,and selenium. Examples of suitable transition metal chalcogenidesinclude, but are not limited to, the electroactive oxides, sulfides, andselenides of transition metals selected from the group consisting of Mn,V, Cr, Ti, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re,Os, and Ir. In one embodiment, the transition metal chalcogenide isselected from the group consisting of the electroactive oxides ofnickel, manganese, cobalt, and vanadium, and the electroactive sulfidesof iron. In one embodiment, the cathode active layer comprises anelectroactive conductive polymer. Examples of suitable electroactiveconductive polymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes.

“Electroactive sulfur-containing materials,” as used herein, relates tocathode active materials which comprise the element sulfur in any form,wherein the electrochemical activity involves the breaking or forming ofsulfur-sulfur covalent bonds. Suitable electroactive sulfur-containingmaterials, include, but are not limited to, elemental sulfur and organicmaterials comprising sulfur atoms and carbon atoms, which may or may notbe polymeric. Suitable organic materials include those furthercomprising heteroatoms, conductive polymer segments, composites, andconductive polymers.

In some embodiments involving Li/S systems, the sulfur-containingmaterial, in its oxidized form, comprises a polysulfide moiety, S_(m),selected from the group consisting of covalent —S_(m)— moieties, ionic—S_(m) ⁻ moieties, and ionic S_(m) ²⁻ moieties, wherein m is an integerequal to or greater than 3. In one embodiment, m of the polysulfidemoiety, S_(m), of the sulfur-containing polymer is an integer equal toor greater than 6. In another embodiment, m of the polysulfide moiety,S_(m), of the sulfur-containing polymer is an integer equal to orgreater than 8. In another embodiment, the sulfur-containing material isa sulfur-containing polymer. In another embodiment, thesulfur-containing polymer has a polymer backbone chain and thepolysulfide moiety, S_(m), is covalently bonded by one or both of itsterminal sulfur atoms as a side group to the polymer backbone chain. Inyet another embodiment, the sulfur-containing polymer has a polymerbackbone chain and the polysulfide moiety, S_(m), is incorporated intothe polymer backbone chain by covalent bonding of the terminal sulfuratoms of the polysulfide moiety.

In one embodiment, the electroactive sulfur-containing materialcomprises greater than 50% by weight of sulfur. In another embodiment,the electroactive sulfur-containing material comprises greater than 75%by weight of sulfur. In yet another embodiment, the electroactivesulfur-containing material comprises greater than 90% by weight ofsulfur.

The nature of the electroactive sulfur-containing materials useful inthe practice of this invention may vary widely, as known in the art. Inone embodiment, the electroactive sulfur-containing material compriseselemental sulfur. In another embodiment, the electroactivesulfur-containing material comprises a mixture of elemental sulfur and asulfur-containing polymer.

In other embodiments, an electrochemical cell described herein includesa composite cathode. The composite cathode may include, for example, (a)an electroactive sulfur-containing cathode material, wherein saidelectroactive sulfur-containing cathode material, in its oxidized state,comprises a polysulfide moiety of the formula —S_(m)—, wherein m is aninteger equal to or greater than 3, as described herein; and, (b) anelectroactive transition metal chalcogenide composition. Theelectroactive transition metal chalcogenide composition may encapsulatethe electroactive sulfur-containing cathode material. In some cases, itmay retard the transport of anionic reduction products of theelectroactive sulfur-containing cathode material. The electroactivetransition metal chalcogenide composition may comprising anelectroactive transition metal chalcogenide having the formula:M_(j)Y_(k)(OR)_(l), wherein M is a transition metal; Y is the same ordifferent at each occurrence and is oxygen, sulfur, or selenium; R is anorganic group and is the same or different at each occurrence; j is aninteger ranging from 1 to 12; k is a number ranging from 0 to 72; and 1is a number ranging from 0 to 72. In some embodiments, k and l cannotboth be 0.

In order to retard out-diffusion of anionic reduction products from thecathode compartment in the cell, a sulfur-containing cathode materialmay be effectively separated from the electrolyte or other layers orparts of the cell by a layer of an electroactive transition metalchalcogenide composition. This layer can be dense or porous.

In one embodiment, a cathode includes a mixture of an electroactivesulfur-containing cathode material, an electroactive transition metalchalcogenide, and optionally binders, electrolytes, and conductiveadditives, which is deposited onto a current collector. In anotherembodiment, a coating of the electroactive sulfur-containing cathodematerial is encapsulated or impregnated by a thin coherent film coatingof the cation transporting, anionic reduction producttransport-retarding, transition metal chalcogenide composition. In yetanother embodiment, a cathode includes particulate electroactivesulfur-containing cathode materials individually coated with anencapsulating layer of the cation transporting, anionic reductionproduct transport-retarding, transition metal chalcogenide composition.Other configurations are also possible.

In one embodiment, a composite cathode includes particulatesulfur-containing cathode materials, generally less than 10 microns indiameter, individually coated with an encapsulating layer of analkali-metal cation-transporting, yet anionic reduction producttransport-retarding electroactive transition metal chalcogenidecomposition. The particle may have a “core-shell” configuration, e.g., acore of an electroactive sulfur-containing cathode material and an outershell of a retarding barrier layer comprising an electroactivetransition metal chalcogenide. Optionally, the composite cathode maycontain fillers comprising various types of binders, electrolytes andconductive materials such as those described herein.

In certain embodiments, the composite cathode is a particulate, porouselectroactive transition metal chalcogenide composition, optionallycontaining non-electroactive metal oxides, such as silica, alumina, andsilicates, that is further impregnated with a soluble electroactivesulfur-containing cathode material. This may be beneficial in increasingthe energy density and capacity compared with cathodes includingelectroactive sulfur-containing cathode material (e.g., electroactiveorgano-sulfur and carbon-sulfur cathode materials) only.

In one set of embodiments, a composite cathode comprises anelectroactive sulfur-containing material (e.g., a carbon-sulfur polymeror elemental sulfur); V₂O₅; conductive carbon; and a PEO binder.

Additional arrangements, components, and advantages of compositecathodes are described in more detail in U.S. Pub. No.: 2006/0115579,filed Jan. 13, 2006, entitled “Novel composite cathodes, electrochemicalcells comprising novel composite cathodes, and processes for fabricatingsame”, which is incorporated herein by reference in its entirety.

Cathodes may further comprise one or more conductive fillers to provideenhanced electronic conductivity. Conductive fillers can increase theelectrically conductive properties of a material and may include, forexample, conductive carbons such as carbon black (e.g., Vulcan XC72Rcarbon black, Printex XE2, or Akzo Nobel Ketjen EC-600 JD), graphitefibers, graphite fibrils, graphite powder (e.g., Fluka #50870),activated carbon fibers, carbon fabrics, non-activated carbonnanofibers. Other non-limiting examples of conductive fillers includemetal coated glass particles, metal particles, metal fibers,nanoparticles, nanotubes, nanowires, metal flakes, metal powders, metalfibers, metal mesh. In some embodiments, a conductive filler may includea conductive polymer. Examples of suitable electroactive conductivepolymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. Other conductive materials known to those of ordinaryskill in the art can also be used as conductive fillers. The amount ofconductive filler, if present, may be present in the range of 2 to 30%by weight of the cathode active layer. The cathodes may also furthercomprise other additives including, but not limited to, metal oxides,aluminas, silicas, and transition metal chalcogenides.

Cathodes may also comprise a binder. The choice of binder material mayvary widely so long as it is inert with respect to the other materialsin the cathode. In some embodiments, the binder material may be apolymeric material. Examples of polymer binder materials include, butare not limited to, polyvinylidene fluoride (PVDF)-based polymers, suchas poly(vinylidene fluoride) (PVDF), PVF₂ and its co- and terpolymerswith hexafluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene,poly(vinyl fluoride), polytetrafluoroethylenes (PTFE),ethylene-tetrafluoroethylene copolymers (ETFE), polybutadiene,cyanoethyl cellulose, carboxymethyl cellulose and its blends withstyrene-butadiene rubber, polyacrylonitrile, ethylene-propylene-diene(EPDM) rubbers, ethylene propylene diene terpolymers, styrene-butadienerubbers (SBR), polyimides or ethylene-vinyl acetate copolymers. In somecases, the binder material may be substantially soluble in aqueous fluidcarriers and may include, but is not limited to, cellulose derivatives,typically methylcellulose (MC), carboxy methylcellulose (CMC) andhydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA),polyacrylic acid salts, polyacryl amide (PA), polyvinyl pyrrolidone(PVP) and polyethylene oxides (PEO). In one set of embodiments, thebinder material ispoly(ethylene-co-propylene-co-5-methylene-2-norbornene) (EPMN), whichmay be chemically neutral (e.g., inert) towards cell components,including polysulfides. UV curable acrylates, UV curable methacrylates,and heat curable divinyl ethers can also be used. The amount of binder,if present, may be present in the range of 2 to 30% by weight of thecathode active layer.

In some embodiments, an electrode described herein comprises aconductive porous support structure and a plurality of particlescomprising sulfur (e.g., as an active species) substantially containedwithin the pores of the support structure. The inventors haveunexpectedly discovered that, in some embodiments, the sizes of thepores within the porous support structure and/or the sizes of theparticles within the pores can be tailored such that the contact betweenthe electrolyte and the sulfur is enhanced, while the electricalconductivity and structural integrity of the electrode are maintained atsufficiently high levels to allow for effective operation of the cell.Also, the sizes of the pores within the porous support structures and/orthe sizes of the particles within the pores can be selected such thatany suitable ratio of sulfur to support material can be achieved whilemaintaining mechanical stability in the electrode. The inventors havealso unexpectedly discovered that the use of porous support structurescomprising certain materials (e.g., metals such as nickel) can lead torelatively large increases in cell performance. In some embodiments,methods for forming particles comprising electrode active material(e.g., comprising sulfur) within pores of a porous support structureallow for a desired relationship between the particle size and poresize. The sizes of the pores within the porous support structure and/orthe sizes of the particles within the pores can also be tailored suchthat the resulting electrode is able to withstand the application of ananisotropic force, while maintaining the structural integrity of theelectrode. Benefits of the application of such forces are describedelsewhere herein.

In developing the systems and methods described herein, the inventorshave identified several challenges associated with producing electrodescomprising sulfur. First, sulfur possesses a relatively low electricalconductivity (e.g., about 5.0×10⁻¹⁴ S cm⁻¹ for elemental sulfur), whichcan inhibit the electrical conductivity of the electrode and hence, cellperformance. In addition, small particle sulfur, which can be useful inproducing uniform thickness and high surface-area electrodes, can bedifficult to produce using traditional mechanical milling, as theparticles that are produced can quickly re-agglomerate. Moreover, highsurface area carbon, which can yield relatively high specific capacityand cycle life, can be difficult to process as a traditional slurrybecause it possesses a high absorption stiffness resulting in a slurrywith a relatively low amount of solids. Finally, traditional slurryprocessing of sulfur-containing electrode materials can lead tore-distribution of the slurry components, which can produce unevenporosity within the cathode and decreased anode utilization. Theinventors have unexpectedly discovered that these traditionaldisadvantages can be overcome by disposing particles comprising sulfurwithin the pores of a support material to produce an electrode thatincludes relatively uniform porosity, particle size, and componentdistribution.

The porous structures described herein, as well as other components andarrangements described herein, can be used in electrochemical cells fora wide variety of devices, such as, for example, electric vehicles,load-leveling devices (e.g., for solar- or wind-based energy platforms),portable electronic devices, and the like. In some cases, the porousstructures described herein may be particularly useful as electrodes insecondary batteries (i.e., rechargeable batteries) such aslithium-sulfur (L-S) batteries.

As used within the context of such porous support structures and theresulting electrodes, a pore is measured using ASTM Standard TestD4284-07, and generally refers to a conduit, void, or passageway, atleast a portion of which is surrounded by the medium in which the poreis formed such that a continuous loop may be drawn around the pore whileremaining within the medium. Generally, voids within a material that arecompletely surrounded by the material (and thus, not accessible fromoutside the material, e.g. closed cells) are not considered pores withinthe context of the set of embodiments dealing with porous supportstructures. In the context of porous support structure embodiments, itshould be understood that, in cases where the article comprises anagglomeration of particles, pores include both the interparticle pores(i.e., those pores defined between particles when they are packedtogether, e.g. interstices) and intraparticle pores (i.e., those poreslying within the envelopes of the individual particles). Pores within aporous support structure may comprise any suitable cross-sectional shapesuch as, for example, circular, elliptical, polygonal (e.g.,rectangular, triangular, etc.), irregular, and the like.

A porous support structure can comprise any suitable form. In someinstances, the porous support structure can comprise a porousagglomeration of discreet particles, within which the particles can beporous or non-porous. For example, the porous support structure might beformed by mixing porous or non-porous particles with a binder to form aporous agglomeration. Electrode active material might be positionedwithin the interstices between the particles and/or the pores within theparticles (in cases where porous particles are employed) to form theinventive electrodes described herein.

In some embodiments, the porous support structure can be a “porouscontinuous” structure. A porous continuous structure, as used herein,refers to a continuous solid structure that contains pores within it,with relatively continuous surfaces between regions of the solid thatdefine the pores. Examples of porous continuous structures include, forexample, a piece of material that includes pores within its volume(e.g., a porous carbon particle, a metal foam, etc.). One of ordinaryskill in the art will be capable of differentiating between a porouscontinuous structure and, for example, a structure which is not a porouscontinuous structure but which is a porous agglomeration of discreetparticles (where the interstices and/or other voids between the discreteparticles would be considered pores) by, for example, comparing SEMimages of the two structures.

In certain embodiments, a porous structure is formed, at least in part,by using a sacrificial filler material, as describe in more detailherein.

The porous support structure may be of any suitable shape or size. Forexample, the support structure can be a porous continuous particle withany suitable maximum cross-sectional dimension (e.g., less than about 10mm, less than about 1 mm, less than about 500 microns, etc.). In somecases, the porous support structure (porous continuous or otherwise) canhave a relatively large maximum cross-sectional dimension (e.g., atleast about 500 microns, at least about 1 mm, at least about 10 mm, atleast about 10 cm, between about 1 mm and about 50 cm, between about 10mm and about 50 cm, or between about 10 mm and about 10 cm). In someembodiments, the maximum cross-sectional dimension of a porous supportstructure within an electrode can be at least about 50%, at least about75%, at least about 90%, at least about 95%, at least about 98%, or atleast about 99% of the maximum cross sectional dimension of theelectrode formed using the porous continuous structure.

In some embodiments, the support structure can be an article with onerelatively thin dimension relative to the other two, such as, forexample, a film. For example, the support structure can be an articlewith a thickness of less than about 1 mm, less than about 500 microns,less than about 100 microns, between about 1 micron and about 5 mm,between about 1 micron and about 1 mm, between about 10 microns andabout 5 mm, or between about 10 microns and about 1 mm, and a widthand/or length at least about 100, at least about 1000, or at least about10,000 times greater. As used herein, the “maximum cross-sectionaldimension” of an article (e.g., a porous support structure) refers tothe largest distance between two opposed boundaries of an article thatmay be measured. Porous support structures described herein may also beof any suitable shape. For example, the support structure can bespherical, cylindrical, or prismatic (e.g., a triangular prism,rectangular prism, etc.). In some cases, the morphology of the supportstructure may be selected such that the support structure can berelatively easily integrated into an electrode for use in, for example,an electrochemical cell. For example, the support structure may comprisea thin film upon which additional components of an electrochemical cell(e.g., an electrolyte, another electrode, etc.) can be formed.

In some cases, porous particles can be used as a porous continuousstructure. In some such embodiments, material (e.g., electrode activematerial) can be deposited within the pores of the particles, and theparticles can be used to form an electrode. For example, porousparticles containing electrode active material within their pores mightbe bound together (e.g., using binder or other additives) to form acomposite electrode. Exemplary processes for forming such compositeelectrodes are described, for example, in U.S. Pub. No.: 2006/0115579,filed Jan. 13, 2006, entitled “Novel composite cathodes, electrochemicalcells comprising novel composite cathodes, and processes for fabricatingsame”, which is incorporated herein by reference in its entirety.

In some embodiments, the porous support structure might comprise arelatively large-scale porous continuous structure that, unlike theporous particles described above, is sized and shaped to serve as anelectrode. Such structures can be formed of a variety of materials suchas, for example, metals (e.g., a metal foam), ceramics, and polymers.Examples of such materials are described in more detail below. In someembodiments, the maximum cross-sectional dimension of a porouscontinuous structure within an electrode can be at least about 50%, atleast about 75%, at least about 90%, at least about 95%, at least about98%, or at least about 99% of the maximum cross sectional dimension ofthe electrode formed using the porous continuous structure.

The use of such relatively large porous continuous structures can, insome embodiments, ensure that little or no binder is located within theelectrode because binder would not be required to hold together smallparticles to form the porous support structure. In some embodiments, theelectrode can include less than about 20 wt %, less than about 10 wt %,less than about 5 wt %, less than about 2 wt %, less than about 1 wt %,or less than about 0.1 wt % binder. In this context, “binder” refers tomaterial that is not an electrode active material and is not included toprovide an electrically conductive pathway for the electrode. Forexample, an electrode might contain binder to facilitate internalcohesion within the cathode.

The porous support structure may comprise any suitable material. In someembodiments, the porous support structure can be used as an electricalconductor within the electrode (e.g., as an electrolyte-accessibleconductive material). Accordingly, the porous support structure maycomprise an electrically conductive material. Examples of electricallyconductive materials that may be suitable for use include, but are notlimited to, metals (e.g., nickel, copper, aluminum, iron, or any othersuitable metal or combination in pure or alloyed form), carbon (e.g.,graphite, carbon black, acetylene black, carbon fibers, carbonnanofibers, hallow carbon tubes, graphene, carbon filaments, etc.),electrically conductive polymers, or any other suitable electricallyconductive material. In some embodiments, the bulk of the porous supportstructure may be formed from an electrically conductive material. Insome cases, the porous support structure may comprise an electricallynon-conductive material that is at least partially coated (e.g., viasolution-based deposition, evaporative deposition, or any other suitabletechnique) with a conductive material. In some embodiments, the poroussupport structure may comprise a glass (e.g., silicon dioxide, amorphoussilica, etc.), a ceramic (e.g., aluminum oxide, tin oxide, vanadiumoxide aerogel, etc.), a semiconductor (e.g., silicon, germanium, galliumarsenide, etc.), non-conductive polymers, and the like.

The porous support structure may comprise pores with a size distributionchosen to enhance the performance of the electrochemical cell. In somecases, the porous support structure may comprise pores than are largerthan sub-nanometer scale and single-nanometer scale pores, which can betoo small to allow for the passage of electrolyte (e.g., liquidelectrolyte) into the pores of the electrode due to, for example,capillary forces. In addition, in some cases, the pores may be smallerthan millimeter-scale pores, which may be so large that they render theelectrode mechanically unstable. In some embodiments, the porous supportstructure can comprise a plurality of pores, wherein each pore of theplurality of pores has a pore volume, and the plurality of pores has atotal pore volume defined by the sum of each of the individual porevolumes. In some embodiments, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total pore volume is occupied by poreshaving cross-sectional diameters of between about 0.1 microns and about20 microns or between about 0.1 microns and about 10 microns. In someembodiments, at least about 50%, at least about 70%, at least about 80%,at least about 90%, at least about 95%, at least about 99%, orsubstantially all of the total pore volume is occupied by pores havingcross-sectional diameters of between about 1 micron and about 10microns, or between about 1 micron and about 3 microns. Stated anotherway, in some embodiments, the plurality of pores of the porous supportstructure together defines a total pore volume, and at least about 50%(or at least about 70%, at least about 80%, at least about 90%, at leastabout 95%, at least about 99%, or substantially all) of the total porevolume is defined by pores having cross-sectional diameters of betweenabout 0.1 microns and about 10 microns (or between about 0.1 microns andabout 20 microns, between about 1 micron and about 10 microns, orbetween about 1 micron and about 3 microns).

In some embodiments, it may be advantageous to use porous materialswherein the plurality of pores has an average cross-sectional diameterwithin a designated range. For example, in some cases, the poroussupport material may comprise a plurality of pores wherein the averagecross-sectional diameter of the plurality of pores is between about 0.1microns and about 20 microns, between about 0.1 microns and about 10microns, between about 1 micron and about 10 microns, or between about 1micron and about 3 microns.

As described below, the pore distributions described herein can beachieved, in some cases, while an anisotropic force (e.g., defining apressure of between about 4.9 Newtons/cm² and about 198 Newtons/cm², orany of the force application ranges outlined herein) is applied to theelectrochemical cell. This can be accomplished by fabricating the poroussupport structure from materials (e.g., metals, ceramics, polymers,etc.) capable of maintaining their porosities under applied loads.Fabricating an electrode from a material which resists deformation underan applied load can allow the electrode to maintains its permeabilityunder pressure, and allows the cathode to maintain the enhanced ratecapabilities described herein. In some embodiments, the yield strengthof the porous support structure (and the resulting electrode producedfrom the porous support structure) can be at least about 200Newtons/cm², at least about 350 Newtons/cm², or at least about 500Newtons/cm². Methods of fabricating such structures are described inmore detail below.

As used herein, the “cross-sectional diameter” of a pore refers to across-sectional diameter as measured using ASTM Standard Test D4284-07.The cross-sectional diameter can refer to the minimum diameter of thecross-section of the pore. The “average cross-sectional diameter” of aplurality of pores refers to the number average of the cross-sectionaldiameters of each of the plurality of the pores.

One of ordinary skill in the art would be capable of calculating thedistribution of cross-sectional diameters and the averagecross-sectional diameter of the pores within a porous structure usingmercury intrusion porosimetry as described in ASTM standard D4284-92,which is incorporated herein by reference in its entirety. For example,the methods described in ASTM standard D4284-92 can be used to produce adistribution of pore sizes plotted as the cumulative intruded porevolume as a function of pore diameter. To calculate the percentage ofthe total pore volume within the sample that is occupied by pores withina given range of pore diameters, one would: (1) calculate the area underthe curve that spans the given range over the x-axis, (2) divide thearea calculated in step (1) by the total area under the curve, and (3)multiply by 100%. Optionally, in cases where the article includes poresizes that lie outside the range of pore sizes that can be accuratelymeasured using ASTM standard D4284-92, porosimetry measurements may besupplemented using BET surface analysis, as described, for example, inS. Brunauer, P. H. Emmett, and E. Teller, J. Am. Chem. Soc., 1938, 60,309, which is incorporated herein by reference in its entirety.

In some embodiments, the porous material may comprise pores withrelatively uniform cross-sectional diameters. Not wishing to be bound byany theory, such uniformity may be useful in maintaining relativelyconsistent structural stability throughout the bulk of the porousmaterial. In addition, the ability to control the pore size to within arelatively narrow range can allow one to incorporate a large number ofpores that are large enough to allow for fluid penetration (e.g.,electrolyte penetration) while maintaining sufficiently small pores topreserve structural stability of the porous material. In someembodiments, the distribution of the cross-sectional diameters of thepores within the porous material can have a standard deviation of lessthan about 50%, less than about 25%, less than about 10%, less thanabout 5%, less than about 2%, or less than about 1% of the averagecross-sectional diameter of the plurality of pores. Standard deviation(lower-case sigma) is given its normal meaning in the art, and can becalculated as:

$\sigma = \sqrt{\frac{\sum\limits_{i = 1}^{n}( {D_{i} - D_{avg}} )^{2}}{n - 1}}$

wherein D_(i) is the cross-sectional diameter of pore i, D_(avg) is theaverage of the cross-sectional diameters of the plurality of pores, andn is the number of pores. The percentage comparisons between thestandard deviation and the average cross-sectional diameters of thepores outlined above can be obtained by dividing the standard deviationby the average and multiplying by 100%.

The electrodes described herein can also comprise a materialsubstantially contained within the pores of the porous supportstructure. A material that is said to be “substantially contained”within a pore is one that at least partially lies within the imaginaryvolume defined by the outer boundaries of the pore. For example, amaterial substantially contained within a pore can be fully containedwithin the pore, or may only have a fraction of its volume containedwithin the pore, but a substantial portion of the material, overall, iscontained within pores. In one set of embodiments, material (e.g.,material comprising sulfur) is provided, at least 30% of which by massis contained within pores of a porous support structure. In otherembodiments, at least 50%, 70%, 80%, 85%, 90%, or 95% by mass of thematerial is contained within the pores of the support structure.

The material within the support structure can comprise, in some cases,particles, which may be substantially solid or porous. In someembodiments, the material substantially contained within the pores maycomprise isolated particles or agglomerated particles. In someembodiments, the material may comprise a film (which may besubstantially solid or porous) on at least a portion of the pores withinthe support structure. In some embodiments, the material maysubstantially fill at least a portion of the pores within the supportstructure, such that the material assumes the shape and/or size of theportion of the pores.

The material within the support structure may comprise, in some cases,an electrode active material such as those described herein. In someembodiments, the electrodes described herein may comprise a relativelylarge amount of material comprising electrode active material within thepores of the porous support. For example, in some embodiments, theelectrode (e.g., cathode, especially a base electrode material layer ofthe cathode) may comprise at least about 20 wt %, at least about 35 wt%, at least about 50 wt %, at least about 65 wt %, or at least about 75wt % material comprising electrode active material, such as theelectroactive sulfur-containing materials described herein.

While sulfur, as the active electrode species, is describedpredominately, it is to be understood that wherever sulfur is describedas the active electrode species herein, any suitable electrode activespecies may be used. Those of ordinary skill in the art will appreciatethis and will be able to select species (e.g., from the list describedbelow) for such use.

In embodiments in which the material within the pores comprisesparticles (e.g., particles of electrode active material), the particlescan be of any suitable shape. For example, in some embodiments, theparticles may be substantially spherical. In some cases, a particle canbe similar in shape to the pore it occupies (e.g., cylindrical,prismatic, etc.).

The size of the particles (e.g., particles of electrode active material)within the pores of the porous support structure can be selected toenhance the performance of the electrochemical cell. In someembodiments, each particle of the plurality of particles within thepores of the porous support structure has a particle volume, and theplurality of particles has a total particle volume defined by the sum ofeach of the individual particle volumes. In addition, in someembodiments, each particle of the plurality of particles within thepores of the porous support structure has a maximum cross-sectionaldimension. In some instances, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total particle volume within the poresof the porous support structure is occupied by particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns. In some embodiments, at least about 50%, at least about 70%, atleast about 80%, at least about 90%, at least about 95%, at least about99%, or substantially all of the total particle volume within the poresof the porous support structure is occupied by particles having maximumcross-sectional dimensions of between about 1 micron and about 10microns, or between about 1 micron and about 3 microns. Stated anotherway, in some embodiments, the plurality of particles together defines atotal quantity of particulate material, and at least about 50% (or atleast about 70%, at least about 80%, at least about 90%, at least about95%, at least about 99%, or substantially all) of the total quantity ofparticulate material is made up of particles having maximumcross-sectional dimensions of between about 0.1 microns and about 10microns (or between about 1 micron and about 10 microns, or betweenabout 1 micron and about 3 microns).

In some embodiments, the particles of material (e.g., electrode activematerial) within the porous support structure may have an averagemaximum cross-sectional dimension within a designated range. Forexample, in some cases, the particles of material (e.g., electrodeactive material) within the porous support structure can have an averagemaximum cross-sectional dimension of between about 0.1 microns and about10 microns, between about 1 micron and about 10 microns, or betweenabout 1 micron and about 3 microns. In some embodiments, the ratio ofthe average maximum cross-sectional dimension of the particles ofmaterial within the porous support structure to the averagecross-sectional diameter of the pores within the porous supportstructure can be between about 0.001:1 and about 1:1, between about0.01:1 and about 1:1, or between about 0.1:1.

In some embodiments, particles within the pores of the porous supportstructure can have relatively uniform maximum cross-sectionaldimensions. Not wishing to be bound by any theory, such uniformity maybe useful in producing relatively consistent performance along a surfaceof an electrode comprising electrode active material particles. In someembodiments, the distribution of the cross-sectional dimensions of thepores within the porous material can have a standard deviation of lessthan about 50%, less than about 25%, less than about 10%, less thanabout 5%, less than about 2%, or less than about 1% of the averagecross-sectional diameter of the plurality of pores. Standard deviation(lower-case sigma) is given its normal meaning in the art, and can becalculated, and expressed as a percentage relative to an average, asdescribed above.

In some embodiments, the material (e.g., particles) within the pores ofthe porous support structure may occupy a relatively large percentage ofthe pore volume. For example, in some embodiments, the material withinthe porous support structure (e.g., particles comprising an electrodeactive material) can occupy at least about 10%, at least about 20%, atleast about 35%, at least about 50%, at least about 70%, or more of theaccessible pore volume of the porous support structure. As used herein,the “accessible pore volume” is consistent with the above definition ofa pore and refers to the percentage of the pore volume that is exposedto the external environment surrounding a porous article, as opposed topore volume that is completely enclosed by the material forming theporous article. The volume occupied by material within the pores shouldbe understood to include an imaginary volume that surrounds the outerboundaries of the material (e.g., particles) within the pores, which mayinclude material (e.g. particle) void volume in cases where the materialwithin the pores is itself porous. One of ordinary skill in the art iscapable of calculating the percentage of accessible pore volume, forexample, using mercury intrusion porosimetry measurements according toASTM Standard Test D4284-07, optionally supplemented by BET surfaceanalysis. The percentage of accessible pore volume within a porousarticle that is occupied by particles can be calculated, for example, byperforming mercury intrusion porosimetry measurements (optionally withBET surface analysis) of the porous article before and after theparticles are positioned within the pores. When the material inside thepores of the support structure is itself porous, mercury intrusionporosimetry measurements (with optional BET surface analysis) may besupplemented with visual analysis of SEM micrographs to determine thevolume occupied by the material (e.g., particles) within the pores.

The electrodes comprising the porous support structure may comprise arelatively high percentage of electrode active material (e.g., sulfur),in some cases. In some embodiments, the electrodes comprising the poroussupport structure can comprise, for example, at least about 20 wt %, atleast about 30 wt %, at least about 40 wt %, or more electrode activematerial. It should be understood that, for the purposes of calculatingthe amount of electrode active material within an electrode, only theweight of the electrode active species is counted. For example, in caseswhere electroactive sulfur-containing materials such as polysulfides ororganic materials comprising sulfur, only the sulfur content of theelectroactive sulfur-containing materials is counted in determining thepercentage of electrode active material within the electrode. In someembodiments, the electrodes comprising the porous support structure cancomprise at least about 20 wt %, at least about 30 wt %, at least about40 wt %, or more sulfur.

Electrodes described herein may have high sulfur loading, relative toknown cells. In some embodiments, the electrode (e.g., a base electrodematerial layer of an electrode) has a sulfur loading of at least 1.0 mgS/cm², at least 1.1 mg S/cm², at least 1.2 mg S/cm², at least 1.3 mgS/cm², at least 1.4 mg S/cm², at least 1.5 mg S/cm² (e.g., 1.6 mgS/cm²), at least 2.5 mg S/cm², at least 5.0 mg S/cm², or, in some cases,greater.

In an illustrative embodiment, the electrode (e.g., a base electrodematerial layer of an electrode) may have a sulfur loading of 4.3 mg/cm²and thickness of less than or equal to about 200 microns, less than orequal to about 150 microns, less than or equal to about 100 microns,less than or equal to about 75 microns, less than or equal to about 50microns, or less than or equal to about 30 microns.

The electrodes described herein can comprise any suitable weight ratioof electrode active material and support material (e.g., any suitableratio of sulfur to carbon). For example, in some embodiments, theelectrode can comprise a weight ratio of sulfur to carbon of at leastabout 1:1, at least about 2:1, at least about 3:1, at least about 4:1,at least about 5:1, or at least about 6:1. In some embodiments, theelectrode can comprise a weight ratio of sulfur to carbon of less thanabout 6:1, less than about 5:1, less than about 4:1, less than about3:1, less than about 2:1, or less than about 1:1.

In some cases, the concentration of the electrode active material (e.g.,sulfur within a cathode) can be relatively consistent across one or moresurfaces of the electrode, or across any cross-section of the electrode.In some embodiments, at least about 50%, at least about 75%, at leastabout 85%, at least about 90%, at least about 95%, or at least about 98%of the area of the surface of an electrode (e.g., cathode) defines auniform area that includes a uniform distribution of electrode activematerial (e.g., sulfur). In some embodiments, at least about 50%, atleast about 75%, at least about 85%, at least about 90%, at least about95%, or at least about 98% of the area of a surface of a cross-sectionsubstantially perpendicular to the thickness of an electrode (e.g., acathode) defines a uniform area that includes a uniform distribution ofelectrode active material (e.g., sulfur). In this context, a “surface ofan electrode” refers to the geometric surface of the electrode, whichwill be understood by those of ordinary skill in the art to refer to thesurface defining the outer boundaries of the electrode, for example, thearea that may be measured by a macroscopic measuring tool (e.g., aruler) and does not include the internal surface area (e.g., area withinpores of a porous material such as a foam, or surface area of thosefibers of a mesh that are contained within the mesh and do not definethe outer boundary, etc.). In addition, a “cross-section of anelectrode” defines an approximate plane viewed by cutting (actually ortheoretically) the electrode to expose the portion one wishes toanalyze. After the electrode has been cut to observe the cross-section,the “surface of the cross-section of the electrode” corresponds to theexposed geometric surface. Stated another way, “surface of an electrode”and “surface of the cross-section of the electrode” refer, respectively,to the geometric surface of the electrode and the geometric surface of across-section of the electrode.

In some embodiments, an electrode active material (e.g., sulfur) isuniformly distributed when any continuous area that covers about 10%,about 5%, about 2%, or about 1% of the uniform area (described in thepreceding paragraphs) includes an average concentration of the electrodeactive material (e.g., sulfur) that varies by less than about 25%, lessthan about 10%, less than about 5%, less than about 2%, or less thanabout 1% relative to the average concentration of the electrode activematerial (e.g., sulfur) across the entirety of the uniform area. In thiscontext, the “average concentration” of an electrode active materialrefers to the percentage of the surface area of the electrode (e.g.,exposed surface area, surface area of a cross section of the electrode)that is occupied by electrode active material when the electrode isviewed from an angle substantially perpendicularly to the electrode.

One of ordinary skill in the art would be capable of calculating averageelectrode active material concentrations within a surface or across-section of an electrode, and the variance in concentrations, byanalyzing, for example, X-ray spectral images of an electrode surface orcross-section. For example, one could obtain an x-ray spectral image ofan electrode surface or cross-section (e.g., by physically slicing theelectrode to produce the cross-section), such as the images shown inFIG. E6A-E6C. To calculate the average concentration of sulfur over agiven area in such an image, one would determine the percentage of theimage that is occupied by the color corresponding to sulfur over thatarea. To determine whether the average concentration within a sub-areavaries by more than X % relative to the average concentration within alarger area, one would use the following formula:

${{Variance}(\%)} = | \frac{C_{L} - C_{sub}}{C_{L}} \middle| {{\cdot 100}\%} $

wherein C_(L) is the average concentration within the larger area(expressed as a percentage), C_(sub) is the average concentration withinthe sub-area (expressed as a percentage). As a specific example, if theaverage concentration of the electrode active material within a sub-areais 12%, and the average concentration of the electrode active materialwithin a larger area is 20%, the variance would be 40%.

Stated another way, in some embodiments, at least about 50% (or at leastabout 75%, at least about 85%, at least about 90%, at least about 95%,or at least about 98%) of the area of the surface of the electrode (orof a cross-section of the electrode) defines a first, continuous area ofessentially uniform sulfur distribution, the first area having a firstaverage concentration of sulfur. In some cases, any continuous area thatcovers about 10% (or about 5%, about 2%, or about 1%) of the first,continuous area of the surface of the electrode (or of the cross sectionof the electrode) includes a second average concentration of sulfur thatvaries by less than about 25% (or less than about 10%, less than about5%, less than about 2%, or less than about 1%) relative to the firstaverage concentration of sulfur across the first, continuous area.

Porous support structures (and resulting electrodes) can be fabricatedusing a variety of methods. For example, in some embodiments, particlescan be suspended in a fluid, and the fluid can be subsequently removed(e.g., via heat drying, vacuum drying, filtration, etc) to produce theporous support structure in which the particles are adhered to eachother. As mentioned above, in some cases, a binder can be used to adhereparticles to form a composite porous support structure.

In some embodiments, porous support structures can be fabricated byheating individual particles of a material until the particles arealtered to form a porous support structure (e.g., a porous continuousstructure). In some embodiments, particles (e.g., metallic particles,ceramic particles, glass particles, etc.) can be arranged such that theyare in contact with each other, with interstices located between theparticles. The particles can then be sintered to form a fused structurein which the interstices between the particles constitute the pores inthe sintered structure. As used herein, “sintering” is given its normalmeaning in the art, and is used to refer to a method for making objectsfrom particles, by heating the particles below their melting point untilthe particles adhere to each other. The total porosity, size of thepores, and other properties of the final structure could be controlledby selecting appropriate particles sizes and shapes, arranging them toform a desired packing density prior to sintering, and selectingappropriate sintering conditions (e.g., heating time, temperature,etc.).

In some cases, particles (e.g., polymeric particles, metallic particles,glass particles, ceramic particles, etc.) particles arranged such thatthey are in contact with each other can be heated such that theparticles melt to form a porous continuous structure. The interstices ofthe original structure can form the pores of the porous continuousstructure in some such embodiments. The total porosity, size of thepores, and other properties of the final structure could be controlledby selecting appropriate particles sizes and shapes, arranging them toform a desired packing density prior to heating, and selectingappropriate heating conditions (e.g., heating time, temperature, etc.).

In some embodiments, the particles can be controllably arranged prior tomelting or sintering. For example, in some cases in which the particlesare used to form a porous layer, it can be advantageous to arrange theparticles such that they are distributed relatively evenly andrelatively flatly against a substrate. This can be achieved, forexample, by suspending the particles in a solvent that is volatile(e.g., at room temperature), and pouring the solvent onto the substrateon which the porous structure is to be formed. After the particlesolvent is deposited, the volatile solvent can be allowed to evaporate,leaving behind a relatively well-ordered array of particles.

The sintering and/or melting processes described herein can be carriedout in a controlled atmosphere, in some cases. For example, the volumein which melting or sintering is performed can be filled with arelatively inter gas (e.g., nitrogen, argon, helium, and the like), insome cases. In some instances, the melting and/or sintering can becarried out in the substantial absence of oxygen, which can reduce oreliminate oxidation and/or combustion of the material used to form theporous support structure. In some embodiments, a reducing atmosphere(e.g., forming gas with the balance nitrogen and/or argon, hydrogen, orthe like) can be used to reduce the final oxygen content of the sinteredand/or melted article.

The sintering and/or melting temperature can be selected based upon thematerial being used to form the porous support structure. For example,when melting particles to form the porous support structure, the heatingtemperature can be selected such that it is above the meltingtemperature of the material from which the particles are made. One ofordinary skill in the art would be capable of selecting an appropriatesintering temperature, based upon the type of material being sintered.For example, suitable sintering temperatures for nickel might be betweenabout 700° C. and about 950° C.

As mentioned above, the sizes and shapes of the particles used to formthe porous support structure can be selected to achieve a desiredporosity. In some embodiments, the particles can be substantiallyspherical, although particles with other cross-sectional shapes (e.g.,ellipses, polygons (e.g., rectangles, triangles, squares, etc.),irregular, etc.) can also be used. The particles can be relatively small(e.g., in the form of a powder), in some embodiments. For example, insome cases, at least about 50%, at least about 70%, at least about 80%,at least about 90%, at least about 95%, at least about 99%, orsubstantially all of the particles have maximum cross-sectionaldimensions of between about 0.5 microns and about 20 microns, betweenabout 1 micron and about 5 microns, between about 1 micron and about 3microns, or between about 3 microns and about 5 microns. Such particlesizes can be useful in producing porous support structures with theadvantageous porosity properties described elsewhere in thisapplication.

In some embodiments, the porous support structure can be formed bycombining a first material with a second material, and forming the poresof the support structure by removing one of the materials from themixture. Removing one of the materials from the mixture can leave behindvoids which ultimately form the pores of the porous support structure.In some cases, the structure of the non-removed material can besubstantially maintained while one or more of the materials within themixture is removed. For example, in some cases, the support structurematerial (e.g., a metal, ceramic, glass, polymer, etc. which might bemelted) or a precursor to the support structure material (e.g., whichmight be converted to form the material of the porous support structurevia, for example, a reaction (e.g., polymerization, precipitation,etc.)), can be mixed with a plurality of templating entities. Thetemplating entities can be arranged such that they form aninterconnected network within the support structure material orprecursor. After the templating entities have been arranged within thesupport structure material, they can be removed from the supportstructure material to leave behind pores. The support structure materialcan be hardened before the templating entities are removed and/or duringthe removal of the templating entities. As used herein, the term“hardened” is used to refer to the process of substantially increasingthe viscosity of a material, and is not necessarily limited tosolidifying a material (although in one set of embodiments, a poroussupport structure material is hardened by converting it into a solid). Amaterial can be hardened, for example, by gelling a liquid phase. Insome instances, a material can be hardened using polymerization (e.g.,IR- or UV-induced polymerization). In some cases, a material can beinghardened can go through a phase change (e.g., reducing the temperatureof a material below its freezing point or below its glass transitiontemperature). A material may also be hardened by removing a solvent froma solution, for example, by evaporation of a solvent phase, therebyleaving behind a solid phase material.

The templating entities can be of any suitable phase. In some cases, thetemplating entities can be solid particles. For example, the templatingentities might comprise silica particles, which can be dissolved out ofa porous structure using, for example, hydrofluoric acid. As anotherexample, the templating entities might comprise ammonium bicarbonate,which can be removed by dissolving it in water. In some embodiments, thetemplating entities can comprise fluid (e.g., liquid and/or gas)bubbles.

The templating entities can also have any suitable shape, regular orirregular, including, but not limited to, spheres, cubes, pyramids, or amixture of these and/or other shapes. The templating entities may alsoeach be formed of any suitable size. In some embodiments, the templatingentities may have an average maximum cross-sectional dimension roughlyequivalent to the size of the desired pores within the porous supportstructure.

As a specific example, a metallic porous support structure can befabricated using metal injection molding. In an exemplary process, a“green” of metal particles, binder, and templating entities can beformed into a suitable structure (e.g., a relatively thin sheet) viainjection molding. As the green is heated, the metal particles can bemelted or sintered together while the binder and templating entities canbe burned off, leaving behind a series of pores.

Porous ceramic structures can also be produced using a templatingmethods. For example, in some cases, a ceramic foam can be produced byincluding ceramic particles and templating entities within a polyaphronsolution (i.e., a bi-liquid foam). The resulting mixture can be used ina sol gel solution, which can form a stable emulsion with the use of,for example, appropriate surfactants. Once the gel has been hardened,the templating entities can be removed by heat treatment. The size ofthe polyaphrons can be controlled by varying the type and amount of thesurfactants in the bi-liquid foam.

Templating methods can also be used to produce porous polymericstructures.

For example, a plurality of solid particles might be dispersed within amonomer solution. After the monomer is polymerized to form a polymer,the solid particles can be selectively dissolved out of the mixture toleave behind a series of pores within the rest of the polymericstructure.

Another method that might be used to produce the porous supportstructures described herein includes 3D printing. 3D printing is knownto those of ordinary skill in the art, and refers to a process by whicha three dimensional object is created by shaping successive layers,which are adhered on top of each other to form the final object. 3Dprinting can be used with a variety of materials, including metals,polymers, ceramics, and others.

A variety of materials (e.g., in particle form, in melt form, or otherforms mentioned herein) can be used to form the porous supportstructure. The material used to form all or part of the porous supportstructure can include a metal or a metal alloy, in some embodiments.Suitable metals include, but are not limited to, nickel, copper,magnesium, aluminum, titanium, scandium, and alloys and/or combinationsof these. In some embodiments, the metal or metal alloy from which theparticles are formed can have a density of less than about 9 g/cm³ orless than about 4.5 g/cm³.

In some embodiments, a polymeric material can be used to form all orpart of the porous support structure. Suitable polymers for use informing porous support structures include, but are not limited to,polyvinyl alcohol (PVA), phenolic resins (novolac/resorcinol), lithiumpolystyrenesulfonate (LiPSS), epoxies, UHMWPE, PTFE, PVDF, PTFE/vinylcopolymers, co-polymers/block co-polymers of the above and others. Insome embodiments, two polymers can be used for their uniquefuncionalities (e.g. PVA for adhesion, and LiPSS for rigidity, orresorcinol for rigidity and an elastomer for flexibility/toughness). Thematerial used to form the porous support structure might include one ormore conductive polymers such as, for example,poly(3,4-ethylenedioxythiphene) (PEDOT), poly(methylenedioxythiophene)(PMDOT), other thiophenes, polyaniline (PANI), polypyrrole (PPy). Thoseof ordinary skill in the art would be capable of selecting a counter ionfor a conductive polymer system, which can be selected from a variety ofchemical species such as PSS for PEDOT, other well known conductivepolymers, and co and block co-polymers as above.

A ceramic material might be used to form all or part of a porous supportstructure, in some instances. Suitable ceramics include, but are notlimited to, oxides, nitrides, and/or oxynitrides of aluminum, silicon,zinc, tin, vanadium, zirconium, magnesium, indium, and/or alloysthereof. In some cases, the porous support structure can include any ofthe oxides, nitrides, and/or oxynitrides above doped to impart desirableproperties, such as electrical conductivity; specific examples of suchdoped materials include tin oxide doped with indium and zinc oxide dopedwith aluminum. The material used to form the porous support structurecan comprise glass (e.g., quartz, amorphous silica, chalcogenides,and/or other conductive glasses) in some embodiments. The porous supportstructure can include, in some cases, aerogels and/or xero gels of anyof the above materials. In some cases, the porous support structure caninclude a vitreous ceramic.

In some embodiments in which the bulk of the porous support structure ismade of a material that is substantially electrically non-conductive,electrically conductive material can be deposited within the pores ofthe support structure to impart electrical conductivity. For example,the bulk of the porous support structure might comprise a ceramic (e.g.,glass) or an electrically non-conductive polymer, and a metal might bedeposited within the pores of the support structure. The electricallyconductive material can be deposited, for example, via electrochemicaldeposition, chemical vapor deposition, or physical vapor deposition. Insome cases, after the deposition of the electrically conductivematerial, an electrode active material can be deposited within the poresof the porous support structure. Suitable materials for placement withinthe pores of the porous support structure to impart electricalconductivity include, but are not limited to carbon and metals such asnickel and copper, and combinations of these.

The bulk of the porous support structure can be made electricallyconductive, in some embodiments, by incorporating one or moreelectrically conductive materials into the bulk of the porous supportstructure material. For example, carbon (e.g., carbon black, graphite orgraphene, carbon fibers, etc.), metal particles, or other electricallyconductive materials might be incorporated into a melt (e.g., anon-conductive polymeric melt, a glass melt, etc.) which is used to forma polymeric porous support structure to impart electrical conductivityto the porous support structure. After the melt is hardened, theelectrically conductive material can be included within the bulk of theporous support structure.

The mechanical properties of the porous support structure can also beenhanced by incorporating materials that structurally reinforce theporous support structure into the bulk of the porous support structure.For example, carbon fibers and/or particulate fillers can beincorporated into a melt (e.g., a metallic melt, a glass melt, apolymeric melt, etc.) which is hardened to form a porous supportstructure. In some cases, carbon fibers and/or particulate fillers canbe incorporated into a solution in which the porous support structure isformed (e.g., in some cases in which the porous support structurecomprises a polymer).

In some embodiments, the surfaces on or within of the porous supportstructure may be activated or modified prior to depositing the material,for example, to provide for enhanced attachment of material to thesurfaces of the porous support structure. Porous support structures canbe activated or modified by exposing the porous material to reactive orunreactive gasses or vapors. In some embodiments, the activation ormodification steps can be performed at elevated temperatures (e.g., atleast about 50° C., at least about 100° C., at least about 250° C., atleast about 500° C., at least about 750° C., or higher) and/oraub-atmospheric pressures (e.g., less than about 760 torr, less thanabout 250 torr, less than about 100 torr, less than about 10 torr, lessthan about 1 torr, less than about 0.1 torr, less than about 0.01 torr,or lower).

Electrode active material (e.g., particles, films, or other formscomprising electrode active material) may be deposited within the poresof the porous support structure via a variety of methods. In someembodiments, electrode active material is deposited by suspending ordissolving a particle precursor (e.g., a precursor salt, elementalprecursor material such as elemental sulfur, and the like) in a solventand exposing the porous support structure to the suspension or solution(e.g., via dipping the porous support structure into the solvent, byspraying the solvent into the pores of the porous support structure, andthe like). The particle precursor may subsequently form particles withinthe pores of the support structure. For example, in some cases, theprecursor may form crystals within the pores of the support structure.Any suitable solvent or suspension medium may be used in conjunctionwith such a technique including aqueous liquids, non-aqueous liquids,and mixtures thereof. Examples of suitable solvents or suspension mediainclude, but are not limited to, water, methanol, ethanol, isopropanol,propanol, butanol, tetrahydrofuran, dimethoxyethane, acetone, toluene,xylene, acetonitrile, cyclohexane, and mixtures thereof. Of course,other suitable solvents or suspension media can also be used as needed.

Electrode active material can also be deposited within the pores of thesupport structure, in some cases, by heating a material above itsmelting point or boiling point (optionally adjusting the surroundingpressure to, for example, aid in evaporation). The heated material maythen be flowed or vaporized into the pores of the support material suchthat particulate deposits or other solids are formed. As a specificexample, elemental sulfur powder can be positioned next to a poroussupport material and heated above the melting point of sulfur, such thatthe sulfur flows into the pores of the material (e.g., via sublimation,via liquid flow). The composite can then be cooled such that the sulfurdeposits within the pores.

In some embodiments, electrode active material can be deposited withinthe pores of the support structure via electrochemical deposition,chemical vapor deposition, or physical vapor deposition. For example,metals such as aluminum, nickel, iron, titanium, and the like, can beelectrochemically deposited within the pores of a porous supportstructure. Alternatively, such materials may be deposited, for example,using a physical vapor deposition technique such as, for example,electron beam deposition.

In some embodiments, catalyst may be deposited within the pores of thesupport structure in addition to the electrode active material (e.g.,before or during the deposition of the electrode active material). Insome cases, the catalyst may catalyze the electrochemical conversion ofthe electrode active material (e.g., the conversion of sulfur to Li₂Sand/or the conversion of Li₂S to sulfur). Suitable catalyst can include,for example, cobalt phthalocyanine and transition metal salts,complexes, and oxides (e.g., Mg_(0.6)Ni_(0.4)O).

In certain embodiments, a porous electrode may be fabricated by using afiller material as a sacrificial material, and removing at least aportion of the filler material. In some cases, incorporation of fillermaterial within a substrate (e.g., a porous carbon material), andsubsequent removal of at least some of the filler material to exposeportions of the substrate, may provide improved accessibility of thesubstrate surface area to other components of the cell. For example, thefiller material may be used to maintain the porosity of an electrodematerial such that the electrolyte may contact interior portions of theelectrode (e.g., pores) during cell operation. In some cases, use of thefiller material during the fabrication of porous electrodes may alsoenhance the accessibility of the active electrode species duringoperation of the cell by increasing the amount of active electrodespecies that is formed on the outer surface of the porous electrode,rather than on the surface of interior pores of the porous electrode.

A wide range of materials may be suitable for use as a filler material,as described herein. In some cases, the filler material may be selectedsuch that it has an affinity for a particular substrate, such as acarbon substrate. In some cases, the filler material be selected suchthat it may be stable (e.g., does not decompose, delaminate, react,dissolve, etc.) during formation of the electrode material and, uponformation of the electrode material, may readily decompose into one ormore gases or vapors, facilitating rapid and complete removal. Those ofordinary skill in the art would be able to identify and select materialsthat exhibit this behavior by, for example, considering the chemicalstructure, or solubility, volatility, and/or vapor pressure of thefiller material at a given temperature.

The filler material may be either a liquid, solid, or combinationthereof. Examples of suitable filler materials include, but are notlimited to, organic and inorganic salts, such as ammonium carbonate,ammonium bicarbonate, and azidocarbonamide, sodium bicarbonate,potassium bicarbonate, sodium carbonate and sodium borohydride. In oneset of embodiments, the filler material is ammonium carbonate orammonium bicarbonate. In some embodiments, the filler material is aliquid, such as water or a hydrocarbon (e.g., octane).

In some cases, the filler material may be combined with a fluid carrierto form a filler solution, which may be applied to the porous substrate.Suitable fluid carriers include aqueous fluid carriers, non-aqueousfluid carriers, and combinations thereof.

In some embodiments, fluid carriers suitable for use in the fillersolution include halogenated or partially halogenated hydrocarbons, suchas methylene chloride, hydrocarbons such as pentane or hexane, aromaticcompounds such as benzene, toluene, or xylene, alcohols such asmethanol, ethanol, isopropanol, other aqueous solvents such as water,mixtures thereof, and the like.

Additional arrangements, components, and advantages of porous electrodesare described in more detail in International Patent Apl. Serial No.PCT/US2009/000090, published as WO2009/089018, filed Jan. 8, 2009,entitled, “Porous Electrodes and Associated Methods” and U.S.Provisional Apl. Ser. No. 61/237,903, filed Aug. 28, 2009, entitled“Electrochemical Cells Comprising Porous Structures Comprising Sulfur”,each of which is incorporated herein by reference in its entirety.

In some embodiments described herein, a force, or forces, is applied toportions of an electrochemical cell. Such application of force mayreduce irregularity or roughening of an electrode surface of the cell,thereby improving performance. The force may comprise, in someinstances, an anisotropic force with a component normal to an activesurface of the anode of the electrochemical cell. In the embodimentsdescribed herein, electrochemical cells (e.g., rechargeable batteries)may undergo a charge/discharge cycle involving deposition of metal(e.g., lithium metal or other active material as described below) on asurface of the anode upon charging and reaction of the metal on theanode surface, wherein the metal diffuses from the anode surface, upondischarging. The uniformity with which the metal is deposited on theanode may affect cell performance. For example, when lithium metal isremoved from and/or redeposited on an anode, it may, in some cases,result in an uneven surface, for example, upon redeposition it maydeposit unevenly forming a rough surface. The roughened surface mayincrease the amount of lithium metal available for undesired chemicalreactions which may result in decreased cycling lifetime and/or poorcell performance. The application of force to the electrochemical cellhas been found, in accordance with embodiments described herein, toreduce such behavior and to improve the cycling lifetime and/orperformance of the cell.

Referring to FIG. 1, a force may be applied in the direction of arrow81. Arrow 82 illustrates the component of the force that is normal to anactive surface 20′ of base electrode material layer 20 (as well asactive surface 35′ of base electrode material layer 35′). In the case ofa curved surface, for example, a concave surface or a convex surface,the force may comprise an anisotropic force with a component normal to aplane that is tangent to the curved surface at the point at which theforce is applied.

In some embodiments, an anisotropic force with a component normal to anactive surface of the anode is applied during at least one period oftime during charge and/or discharge of the electrochemical cell. In someembodiments, the force may be applied continuously, over one period oftime, or over multiple periods of time that may vary in duration and/orfrequency. The anisotropic force may be applied, in some cases, at oneor more pre-determined locations, optionally distributed over an activesurface of the anode. In some embodiments, the anisotropic force isapplied uniformly over one or more active surfaces of the anode.

An “anisotropic force” is given its ordinary meaning in the art andmeans a force that is not equal in all directions. A force equal in alldirections is, for example, internal pressure of a fluid or materialwithin the fluid or material, such as internal gas pressure of anobject. Examples of forces not equal in all directions include forcesdirected in a particular direction, such as the force on a table appliedby an object on the table via gravity. Another example of an anisotropicforce includes a force applied by a band arranged around a perimeter ofan object. For example, a rubber band or turnbuckle can apply forcesaround a perimeter of an object around which it is wrapped. However, theband may not apply any direct force on any part of the exterior surfaceof the object not in contact with the band. In addition, when the bandis expanded along a first axis to a greater extent than a second axis,the band can apply a larger force in the direction parallel to the firstaxis than the force applied parallel to the second axis.

A force with a “component normal” to a surface, for example an activesurface of an anode, is given its ordinary meaning as would beunderstood by those of ordinary skill in the art and includes, forexample, a force which at least in part exerts itself in a directionsubstantially perpendicular to the surface. Those of ordinary skill canunderstand other examples of these terms, especially as applied withinthe description of this document.

In some embodiments, the anisotropic force can be applied such that themagnitude of the force is substantially equal in all directions within aplane defining a cross-section of the electrochemical cell, but themagnitude of the forces in out-of-plane directions is substantiallyunequal to the magnitudes of the in-plane forces.

In one set of embodiments, cells described herein are constructed andarranged to apply, during at least one period of time during chargeand/or discharge of the cell, an anisotropic force with a componentnormal to the active surface of the anode. Those of ordinary skill inthe art will understand the meaning of this. In such an arrangement, thecell may be formed as part of a container which applies such a force byvirtue of a “load” applied during or after assembly of the cell, orapplied during use of the cell as a result of expansion and/orcontraction of one or more portions of the cell itself.

The magnitude of the applied force is, in some embodiments, large enoughto enhance the performance of the electrochemical cell. An anode activesurface and the anisotropic force may be, in some instances, togetherselected such that the anisotropic force affects surface morphology ofthe anode active surface to inhibit increase in anode active surfacearea through charge and discharge and wherein, in the absence of theanisotropic force but under otherwise essentially identical conditions,the anode active surface area is increased to a greater extent throughcharge and discharge cycles. “Essentially identical conditions,” in thiscontext, means conditions that are similar or identical other than theapplication and/or magnitude of the force. For example, otherwiseidentical conditions may mean a cell that is identical, but where it isnot constructed (e.g., by brackets or other connections) to apply theanisotropic force on the subject cell.

In some embodiments, an anisotropic force with a component normal to anactive surface of the anode is applied, during at least one period oftime during charge and/or discharge of the cell, to an extent effectiveto inhibit an increase in surface area of the anode active surfacerelative to an increase in surface area absent the anisotropic force.The component of the anisotropic force normal to the anode activesurface may, for example, define a pressure of at least about 4.9, atleast about 9.8, at least about 24.5, at least about 49, at least about78, at least about 98, at least about 117.6, at least about 147, atleast about 175, at least about 200, at least about 225, or at leastabout 250 Newtons per square centimeter. In some embodiments, thecomponent of the anisotropic force normal to the anode active surfacemay, for example, define a pressure of less than about 250, less thanabout 225, less than about 196, less than about 147, less than about117.6, less than about 98, less than about 49, less than about 24.5, orless than about 9.8 Newtons per square centimeter. In some cases, thecomponent of the anisotropic force normal to the anode active surface ismay define a pressure of between about 4.9 and about 147 Newtons persquare centimeter, between about 49 and about 117.6 Newtons per squarecentimeter, between about 68.6 and about 98 Newtons per squarecentimeter, between about 78 and about 108 Newtons per squarecentimeter, between about 4.9 and about 250 Newtons per squarecentimeter, between about 49 and about 250 Newtons per squarecentimeter, between about 80 and about 250 Newtons per squarecentimeter, between about 90 and about 250 Newtons per squarecentimeter, or between about 100 and about 250 Newtons per squarecentimeter. The force or pressure may, in some embodiments, beexternally-applied to the cell, as described herein. While forces andpressures are generally described herein in units of Newtons and Newtonsper unit area, respectively, forces and pressures can also be expressedin units of kilograms-force (kgf) and kilograms-force per unit area,respectively. One or ordinary skill in the art will be familiar withkilogram-force-based units, and will understand that 1 kilogram-force isequivalent to about 9.8 Newtons.

As described herein, in some embodiments, the surface of a baseelectrode layer can be enhanced during cycling (e.g., for lithium, thedevelopment of mossy or a rough surface of lithium may be reduced oreliminated) by application of an externally-applied (in someembodiments, uniaxial) pressure. The externally-applied pressure may, insome embodiments, be chosen to be greater than the yield stress of amaterial forming the base electrode material layer. For example, for abase electrode material comprising lithium, the cell may be under anexternally-applied anisotropic force with a component defining apressure of at least about 8 kgf/cm², at least about 9 kgf/cm², or atleast about 10 kgf/cm². This is because the yield stress of lithium isaround 7-8 kgf/cm². Thus, at pressures (e.g., uniaxial pressures)greater than this value, mossy Li, or any surface roughness at all, maybe reduced or suppressed. The lithium surface roughness may mimic thesurface that is pressing against it. Accordingly, when cycling under atleast about 8 kgf/cm², at least about 9 kgf/cm², or at least about 10kgf/cm² of externally-applied pressure, the lithium surface may becomesmoother with cycling when the pressing surface is smooth. As describedherein, the pressing surface may be modified by choosing the appropriatematerial(s) positioned between the anode and the cathode. For instance,in some cases the smoothness of the lithium surface (or surface of otheractive electrode materials) can be increased, during application ofpressure, by the use of a polymer gel layer as described herein.

In some cases, one or more forces applied to the cell have a componentthat is not normal to an active surface of an anode. For example, inFIG. 1, force 84 is not normal to anode active surface 20′. In one setof embodiments, the sum of the components of all applied anisotropicforces in a direction normal to the anode active surface is larger thanany sum of components in a direction that is non-normal to the anodeactive surface. In some embodiments, the sum of the components of allapplied anisotropic forces in a direction normal to the anode activesurface is at least about 5%, at least about 10%, at least about 20%, atleast about 35%, at least about 50%, at least about 75%, at least about90%, at least about 95%, at least about 99%, or at least about 99.9%larger than any sum of components in a direction that is parallel to theanode active surface.

In some embodiments, the cathode and anode have yield stresses, whereinthe effective yield stress of one of the cathode and anode is greaterthan the yield stress of the other, such that an anisotropic forceapplied normal to the surface of one of the active surface of the anodeand the active surface of the cathode causes the surface morphology ofone of the cathode and the anode to be affected. In some embodiments,the component of the anisotropic force normal to the anode activesurface is between about 20% and about 200% of the yield stress of theanode material, between about 50% and about 120% of the yield stress ofthe anode material, between about 80% and about 120% of the yield stressof the anode material, between about 80% and about 100% of the yieldstress of the anode material, between about 100% and about 300% of theyield stress of the anode material, between about 100% and about 200% ofthe yield stress of the anode material, or between about 100% and about120% of the yield stress of the anode material.

The anisotropic force described herein may be applied using any suitablemethod known in the art. In some embodiments, the force may be appliedusing compression springs. For example, referring to FIG. 1,electrochemical cell 10 may be situated in an optional enclosedcontainment structure 90 with one or more compression springs situatedbetween surface 91 and the adjacent wall of the containment structure toproduce a force with a component in the direction of arrow 82. In someembodiments, the force may be applied by situating one or morecompression springs outside the containment structure such that thespring is located between an outside surface 92 of the containmentstructure and another surface (e.g., a tabletop, the inside surface ofanother containment structure, an adjacent cell, etc.). Forces may beapplied using other elements (either inside or outside a containmentstructure) including, but not limited to Belleville washers, machinescrews, pneumatic devices, and/or weights, among others. For example, inone set of embodiments, one or more cells (e.g., a stack of cells) arearranged between two plates (e.g., metal plates). A device (e.g., amachine screw, a spring, etc.) may be used to apply pressure to the endsof the cell or stack via the plates. In the case of a machine screw, forexample, the cells may be compressed between the plates upon rotatingthe screw. As another example, in some embodiments, one or more wedgesmay be displaced between a surface of the cell (or the containmentstructure surrounding the cell) and a fixed surface (e.g., a tabletop,the inside surface of another containment structure, an adjacent cell,etc.). The anisotropic force may be applied by driving the wedge betweenthe cell and the adjacent fixed surface through the application of forceon the wedge (e.g., by turning a machine screw).

In some cases, cells may be pre-compressed before they are inserted intocontainment structures, and, upon being inserted to the containmentstructure, they may expand to produce a net force on the cell. Such anarrangement may be advantageous, for example, if the cell is capable ofwithstanding relatively high variations in pressure. In suchembodiments, the containment structures may comprise a relatively highstrength (e.g., at least about 100 MPa, at least about 200 MPa, at leastabout 500 MPa, or at least about 1 GPa). In addition, the containmentstructure may comprise a relatively high elastic modulus (e.g., at leastabout 10 GPa, at least about 25 GPa, at least about 50 GPa, or at leastabout 100 GPa). The containment structure may comprise, for example,aluminum, titanium, or any other suitable material.

In some cases, any of the forces described herein may be applied to aplurality of electrochemical cells in a stack. As used herein, a “stack”of electrochemical cells is used to refer to a configuration in whichmultiple cells are arranged in an essentially cell-repetitive pattern,e.g., positioned on top of one another. In some cases, the cells may bepositioned such that at least one surface of each cell in the stack issubstantially parallel to at least one surface of every other cell inthe stack, e.g., where a surface of one particular component (e.g., theanode) of one cell is substantially parallel to the same surface of thesame component of every other cell. In some embodiments, the cells maybe in direct contact with one another, while in some instances one ormore spacers may be positioned between the cells in a stack. The stackof electrochemical cells may comprise any suitable number of cells(e.g., at least 2, at least 3, at least 5, at least 10, at least 25, atleast 100 cells, or more).

In some embodiments, a constricting element may surround at least aportion of a cell or a stack of cells. The constricting element may beconstructed and arranged, in some cases, to apply an anisotropic forcewith a component normal to at least one anode active surface within thecell or stack of cells defining a pressure of at least about 4.9, atleast about 9.8, at least about 24.5, at least about 49, at least about98, at least about 117.6, at least about 147, less than about 196, lessthan about 147, less than about 117.6, less than about 98, less thanabout 49, less than about 24.5, less than about 9.8, between about 4.9and about 147, between about 49 and about 117.6, or between about 68.6and about 98 Newtons per square centimeter.

In some embodiments, the constricting element may comprise a band (e.g.,a rubber band, a turnbuckle band, etc.). In some embodiments, a band canbe affixed to the cell or stack of cells by, for example adhesive,staples, clamps, a turn-buckle, or any other suitable method.

In some embodiments, the mass density of the elements used to apply aforce to a cell or a stack of cells (e.g., a constricting element, anexpanding element, etc.) is relatively low. By using elements withrelatively low mass densities, the energy density and specific energy ofthe cell or stack of cells may remain relatively high, In someembodiments the mass density of the article(s) used to apply a force toa cell or a stack of cells is less than about 10 g/cm³, less than about5 g/cm³, less than about 3 g/cm³, less than about 1 g/cm³, less thanabout 0.5 g/cm³, less than about 0.1 g/cm³, between about 0.1 g/cm³ andabout 10 g/cm³, between about 0.1 g/cm³ and about 5 g/cm³, or betweenabout 0.1 g/cm³ and about 3 g/cm³.

In some embodiments, pressure distribution components may be includedbetween a cell and another cell or between a cell and a constrictingelement. Such pressure distribution components can allow for a uniformforce to be applied throughout the cell or stack of cells. In somecases, the pressure distribution components comprise an end cap. The endcaps' shape can be selected so as to convert the linear forces appliedby the band to a uniform force across, for example, the active area ofan anode.

In some embodiments, the mass density of the end caps may be relativelylow. For example, the end caps may have a mass density of less thanabout 5 g/cm³, less than about 3 g/cm³, less than about 1 g/cm³, lessthan about 0.5 g/cm³, less than about 0.1 g/cm³, between about 0.1 g/cm³and about 10 g/cm³, between about 0.1 g/cm³ and about 5 g/cm³, orbetween about 0.1 g/cm³ and about 3 g/cm³. In addition, the end caps maycomprise any suitable stiffness. For example, the stiffness of the endcaps may be higher than 50 GPa, in some embodiments.

Another example of a pressure distribution component comprises a spacerpositioned between two cells. Inter-cell spacers can serve to reducestress concentrations that may arise, for example, due to geometricalmanufacturing variations of individual cells. For example, the flatnessof the cells may vary from cell to cell. As another example, opposingsides of one or more cells may not be perfectly parallel in some cases.

A spacer can also have any suitable thickness. In some cases, a spacermay have an average thickness of less than about 10 mm, less than about5 mm, less than about 1 mm, less than about 500 microns, or less thanabout 250 microns. In some embodiments, a spacer can be between about100 microns and about 10 mm, between about 100 microns and about 1 mm,between about 250 microns and about 10 mm, between about 250 microns andabout 1 mm, or between about 500 microns and about 2 mm.

Opposing faces of the spacer(s) may be highly parallel, in someembodiments. For example, in some embodiments, the variation of thedistance between a first surface of a spacer in contact with a firstcell and a second surface of the spacer in contact with a second cell,as measured substantially parallel to a vector drawn from the center ofmass of the first cell to the center of mass of the second cell, acrossthe width of the spacer is less than about 1 mm, less than about 500microns, less than about 100 microns, less than about 50 microns, lessthan about 25 microns, less than about 10 microns, or less than about 1micron.

The mass density of the spacer(s) in a stack of cells can be relativelylow, in some instances. For example, the spacers may have a mass densityof less than about 5 g/cm³, less than about 2 g/cm³, less than about 1g/cm³, less than about 0.5 g/cm³, less than about 0.1 g/cm³, betweenabout 0.1 g/cm³ and about 10 g/cm³, between about 0.1 g/cm³ and about 5g/cm³, or between about 0.1 g/cm³ and about 2 g/cm³. In addition, theend caps may comprise a relatively high stiffness. For example, thestiffness of the spacer(s) may be higher than 10 GPa, in someembodiments.

The use of constriction elements is not limited to flat cell geometries.In some instances, a constriction element may be used to apply a forceto a cylindrical electrochemical cell or a prismatic electrochemicalcell (e.g., a triangular prism, a rectangular prism, etc.).

Any of the constriction elements described above may be used asconstriction elements in cylindrical cells, prismatic cells, or othersuch cells. For example, in some embodiments, one or more wraps of thesame or different winding material may be positioned on the outsidesurface of the cell. In some embodiments, the winding material comprisesrelatively high strength. The winding material may also comprise arelatively high elastic modulus. In some cases, shrink wrap tubing suchas polyester film and fabric. In some cases, the constriction elementcomprises an elastic material properly sized to provide requiredexternal pressure after it relaxes on the outer surface of the cell.

In some embodiments, the cell may comprise an expanding element (e.g.,an expanding mandrel) within an inner volume of the cell. The expandingelement can be constructed and arranged to apply a force radiatingoutward from the inner volume of the electrochemical cell. In someembodiments, the expanding element and the constricting element can beconstructed and arranged such that the force (e.g., pressure) at eachpoint within the boundaries of the electrochemical cell deviates by lessthan about 30%, less than about 20%, less than about 10%, or less thanabout 5% of the average force (e.g., pressure) within the boundarieselectrochemical cell. In some embodiments, such a distribution of forcescan be achieved, for example, by selecting constricting and expandingelements such that substantially equal internal and external forces perunit area are applied to the cell.

In some embodiments, rather than applying an internal force to define apressure, external force application can be combined with complimentarywinding mechanics to achieve a radial pressure distribution that iswithin acceptable bounds. In some embodiments, the total volumes of thepressure distribution elements(s) (e.g., end caps, spacers, etc.) andthe element(s) used to apply a force to the cell or stack of cells(e.g., bands, mandrels, etc.) may be relatively low. By employing lowvolumes, the energy density of the assembly may be kept relatively high.In some cases, the sum of the volumes of the pressure distributionelement(s) and the element(s) used to apply a force to a cell or stackof cells comprises less than about 10%, less than about 5%, less thanabout 2%, less than about 1%, less than about 0.5%, less than about0.1%, between about 0.1% and about 10%, between about 0.1% and about 5%,between about 0.1% and about 2%, or between about 0.1% and about 1% ofthe volume of the cell or stack of cells.

In some cases, the cells described herein may change size (e.g., swell)during charge and discharge. When selecting the method of applying theanisotropic force, it may be desirable, in some embodiments, to selectmethods that produce a relatively constant force as the cell changesshape and/or size during charge and discharge. In some instances, thisselection may be analogous to selecting a system with a low effectivespring constant (e.g., a “soft” spring). For example, when using acompression spring to apply the anisotropic force, a spring with arelatively low spring constant may produce an anisotropic force that ismore constant during cell cycling than the force produced by a springwith a relatively high spring constant. In cases where elastic bands areused, a band with a relatively high elasticity may produce ananisotropic force that is more constant during cell cycling than theforce produced by a band with a relatively low elasticity. In someembodiments in which force is applied using a machine screw, the use ofsoft screws (e.g., brass, polymer, etc.) may be advantageous. In someapplications, for example, a machine screw may be selected to cover adesired range of compression, but the screw itself may be soft.

In some embodiments, the electrochemical cells described herein areplaced in containment structures, and at least a portion of ananisotropic force with a component normal to the active surface of theanode is produced due to the expansion of the electrochemical cellrelative to the containment structure. In some cases, the containmentstructure is sufficiently rigid such that it does not deform during theexpansion of the electrochemical cell, resulting in a force applied onthe cell. The electrochemical cell may swell as the result of a varietyof phenomena. For example, in some cases, the electrochemical cell mayundergo thermal expansion. In some embodiments, the electrochemical cellmay swell due to charge and/or discharge of the cell. For example, insome cases, a partially discharged cell may be placed in a containmentstructure. Upon charging the partially discharged cell, the cell mayswell. This expansion may be limited by the dimensions of thecontainment structure, resulting in the application of an anisotropicforce.

In some cases, the cell may swell due to the adsorption of a liquid intoporous components of the electrochemical cell. For example, in someembodiments, a dry porous electrochemical cell may be placed within acontainment structure. The dry porous electrochemical cell may then besoaked (e.g., with a liquid electrolyte). In some cases, the propertiesof the electrolyte (e.g., surface tension) and the electrochemical cell(e.g., size of the porous cavities) may be selected such that, when theelectrochemical cell is wetted by the electrolyte, a desirable level ofcapillary pressure is generated. Once wetted, the electrode stack willswell, thus generating an anisotropic force. At equilibrium, theanisotropic force exerted by the containment structure on theelectrochemical cell will be equal to the force resulting from thecapillary pressure.

Containment structures described herein may comprise a variety of shapesincluding, but not limited to, cylinders, prisms (e.g., triangularprisms, rectangular prisms, etc.), cubes, or any other shape. In someembodiments, the shape of the containment structure is chosen such thatthe walls of the containment structure are parallel to the outersurfaces of the electrochemical cell. For example, in some cases, thecontainment structure may comprise a cylinder, which can be used, forexample, to surround and contain a cylindrical electrochemical cell. Inother instances, the containment structure may comprise a prismsurrounding a similarly shaped prismatic electrochemical cell.

In some embodiments, the application of a force as described herein mayallow for the use of smaller amounts of anode active material (e.g.,lithium) and/or electrolyte within an electrochemical cell, relative tothe amounts used in essentially identical cells in which the force isnot applied. In cells lacking the applied force described herein, anodeactive material (e.g., lithium metal) may be, in some cases, redepositedunevenly on an anode during charge-discharge cycles of the cell, forminga rough surface. In some cases, this may lead to an increase in therates of one or more undesired reactions involving the anode metal.These undesired reactions may, after a number of charge-dischargecycles, stabilize and/or begin to self-inhibit such that substantiallyno additional anode active material becomes depleted and the cell mayfunction with the remaining active materials. For cells lacking theapplied force as described herein, this “stabilization” is often reachedonly after a substantial amount of anode active material has beenconsumed and cell performance has deteriorated. Therefore, in some caseswhere forces as described herein have not been applied, a relativelylarge amount of anode active material and/or electrolyte has often beenincorporated within cells to accommodate for loss of material duringconsumption of active materials, in order to preserve cell performance.

Accordingly, the application of force as described herein may reduceand/or prevent depletion of active materials such that the inclusion oflarge amounts of anode active material and/or electrolyte within theelectrochemical cell may not be necessary. For example, the force may beapplied to a cell prior to use of the cell, or in an early stage in thelifetime of the cell (e.g., less than five charge-discharge cycles),such that little or substantially no depletion of active material mayoccur upon charging or discharging of the cell. By reducing and/oreliminating the need to accommodate for active material loss duringcharge-discharge of the cell, relatively small amounts of anode activematerial may be used to fabricate cells and devices as described herein.In some embodiments, devices described herein comprise anelectrochemical cell having been charged and discharged less than fivetimes in its lifetime, wherein the cell comprises an anode, a cathode,and an electrolyte, wherein the anode comprises no more than five timesthe amount of anode active material which can be ionized during one fulldischarge cycle of the cell. In some cases, the anode comprises no morethan four, three, two, or 1.5 times the amount of lithium which can beionized during one full discharge cycle of the cell.

In some embodiments, the application of force, as described herein, mayresult in improved capacity after repeated cycling of theelectrochemical cell. For example, in some embodiments, afteralternatively discharging and charging the cell three times, the cellexhibits at least about 50%, at least about 80%, at least about 90%, orat least about 95% of the cell's initial capacity at the end of thethird cycle. In some cases, after alternatively discharging and chargingthe cell ten times, the cell exhibits at least about 50%, at least about80%, at least about 90%, or at least about 95% of the cell's initialcapacity at the end of the tenth cycle. In still further cases, afteralternatively discharging and charging the cell twenty-five times, thecell exhibits at least about 50%, at least about 80%, at least about90%, or at least about 95% of the cell's initial capacity at the end ofthe twenty-fifth cycle.

In some embodiments, the use of a cathode that is resistant tocompression can enhance the performance of the cell relative to cells inwhich the cathode is significantly compressible. Not wishing to be boundby any theory, the use of elastic, relatively highly compressiblecathodes may result in the evacuation of liquid electrolyte during theapplication of the anisotropic force. The evacuation of liquidelectrolyte from the cathode may result in decreased power output duringthe operation of the electrochemical cell. For example, in some cases adecrease in power output from the electrochemical cell may be observedeven when the anisotropic force is relatively small (e.g., ananisotropic force with a component normal to an active surface of theanode defining a pressure of about 68.6 Newtons/cm²) or when theanisotropic force is of another magnitude, for example, as noted abovewith reference to limits and ranges of the component of the anisotropicforce normal to the anode active surface. The degree of compressibilitycan be correlated to a change in porosity, i.e., change in void volumeof the cathode, during application of a compressive force. In someembodiments, it may be desirable to limit the change in porosity of thecathode during the operation of the cell. For example, in someembodiments of the invention, the porosity of the cathode may bedecreased during operation of the cell by less than 10%, less than 6%,less than 4%, less than 2%, less than 1%, less than 0.5%, less than0.1%, or lower. That is, during use of the cell, a compressive forceexperienced by the cathode may reduce the total void volume, or totalvolume otherwise accessible by the electrolyte, by percentages notedabove, where the cathode is fabricated to provide suitable resistance tocompression.

The stiffness of the cathode (resistance to compressibility) may beenhanced using a variety of methods. In some embodiments, the type ofelectrolyte and the size of the pores in the cathode may be togetherselected such that the resulting capillary forces produced by theinteraction of the electrolyte and the cathode pores resist thedeformation of the cathode. This effect may be particularly useful, forexample, in small electrochemical cells. As another example, thestiffness of the cathode may be enhanced by incorporating reinforcementfibers (e.g., to connect carbon particles) into the cathode. In somecases, binder may be incorporated into the cathode to provide rigidity.In other embodiments, an inherently rigid cathode may be produced byinfusing active material (e.g., reticulated Ni foam) into a thin andlight superstructure.

Additional arrangements, components, and advantages of applying one ormore forces to an electrochemical described herein are provided in U.S.patent application Ser. No. 12/535,328, filed Aug. 4, 2009, entitled“Application of Force In Electrochemical Cells”, published as U.S. Pub.No. 2010/0035128, which is incorporated herein by reference in itsentirety.

Certain cathodes used in lithium metal rechargeable batteries mayinclude a carbon-based component, sulfur, and a binder or other materialof some sort to facilitate internal cohesion of the cathode. In someembodiments, application of pressure to a cathode before and/or duringuse (e.g., cycling) can reduce the need for binder or other adhesivewhich can increase the overall surface area of carbon available forfacilitating both internal electrode conductivity and electricalcommunication with sulfur, and with electrolyte to which the cathode isexposed. Thus, even if void volume of a cathode is reduced byapplication of pressure (i.e., reduction of a volume within the cathodewhich can be taken up by electrolyte), relative to an essentiallyidentical cathode absent application of this pressure, performance ofthe cathode and an overall device utilizing the cathode can be improved.The cathodes described herein may possess enhanced properties thatrender them particularly suitable for use in electrochemical cellsdesigned to be charged and/or discharged while a force is applied. Thecathodes described herein may retain their mechanical integrity whencharged and/or discharged during the application of an anisotropic force(e.g., defining a pressure of about 196 Newtons per square centimeter orgreater). In some embodiments, the cathode retains sufficient porosityto charge and discharge effectively when a force is applied to the cell.Cathodes described herein may also comprise relatively highelectrolyte-accessible conductive material (e.g., carbon) areas. Thecathode may comprise a relatively low ratio of the amount of binderand/or mass of electrolyte to cathode active material (e.g., sulfur)ratio in some instances. In some embodiments, electrochemical cellscomprising the cathodes described herein may achieve relatively highspecific capacities and/or relatively high discharge current densities.In addition, the cathodes described herein may exhibit relatively highcathode active material (e.g., sulfur) utilization during charge anddischarge. In still further cases, the electrical conductivity betweenconductive material in the cathode (e.g., carbon) may be enhanced duringthe application of the force.

Cathodes described herein may comprise one or more properties thatrender them effective in delivering enhanced performance. In someinstances, the cathodes may exhibit one or more of the propertiesoutlined below during the application of an anisotropic force, themagnitude of which may lie within any of the ranges described herein.

In certain embodiments, cathodes described herein may exhibit relativelyhigh porosities. In some cases, the porosity of the cathode may be atleast about 30%, at least about 40%, at least about 50%, at least about60%, at least about 70%, at least about 80%, or at least about 90%. Suchporosities may be retained, in some cases, while an anisotropic force(e.g., defining a pressure of between about 4.9 and about 196 Newtonsper square centimeter, or any of the ranges outlined below) is appliedto the electrochemical cell. As used herein, the “porosity” of anelectrode (e.g., the cathode) is defined as the void volume of theelectrode divided by the volume within the outer boundary of theelectrode, and is expressed as a percentage. “Void volume” is used torefer to portions of the cathode that are not occupied by cathode activematerial (e.g., sulfur), conductive material (e.g., carbon), binder, orother materials that provide structural support. The void volume withinthe cathode may comprise pores in the cathode as well as intersticesbetween aggregates of the cathode material. Void volume may be occupiedby electrolyte, gases, or other non-cathode materials. In someembodiments, the void volume of the cathode may be at least about 1, atleast about 2, at least about 4, or at least about 8 cm³ per gram ofcathode active material (e.g., sulfur) in the cathode. In someinstances, the void volume may comprise pores with relatively largediameters. For example, in some embodiments, pores of a diameter of atleast about 200 nm constitute at least about 50% of the void volume inthe cathode.

As noted above, in some embodiments, compressing a cathode facilitatescathode integrity, where the cathode has relatively less binder oradhesive than otherwise might be required to maintain integrity, andsuch compression may improve performance of the cathode and/or a deviceinto which the cathode is incorporated. This improvement can be realizedeven if void volume of the cathode (and/or the relative amount ofelectrolyte present in the cathode during use) is reduced. It can alsobe useful, in combination with embodiments described herein, to select acathode that is resistant to compression to enhance the performance ofthe cell relative to cells in which the cathode is significantlycompressible. For example, using a compression resistant cathode mayhelp maintain high porosities or void volumes during the application ofan anisotropic force to the cell. Not wishing to be bound by any theory,the use of elastic, relatively highly compressible cathodes may resultin the evacuation of liquid electrolyte during the application of theanisotropic force. The evacuation of liquid electrolyte from the cathodemay result in decreased power output during the operation of theelectrochemical cell. The use of compressible cathodes may cause adecrease in power output from the electrochemical cell even when theanisotropic force is relatively small (e.g., an anisotropic forcedefining a pressure of about 68.6 Newtons per square centimeter) or whenthe anisotropic force is of another magnitude, for example, as notedbelow with reference to limits and ranges of the component of theanisotropic force normal to the anode active surface.

The degree of compressibility can be correlated to a change in porosity,i.e., change in void volume of the cathode, during application of acompressive force. In some embodiments, it may be desirable to limit thechange in porosity of the cathode during the operation of the cell. Forexample, in some embodiments of the invention, the porosity of thecathode may be decreased during operation of the cell by less than about10%, less than about 6%, less than about 4%, less than about 2%, lessthan about 1%, less than about 0.5%, less than about 0.1%, or lower.That is, during use of the cell, a compressive force experienced by thecathode may reduce the total void volume, or total volume otherwiseaccessible by the electrolyte, by percentages noted above, where thecathode is fabricated to provide suitable resistance to compression.Electrochemical cells and other devices comprising cathodes describedherein may achieve high levels of performance despite having lowerporosities during the application of a force than would be observedabsent the force.

The stiffness of the cathode (resistance to compressibility) may beenhanced using a variety of methods. In some embodiments, the cathodemay comprise one or more binder materials (e.g., polymers, porous silicasol-gel, etc.) which may, among other functions, provide rigidity.Examples of suitable binders for use in cathodes are described hereinand may include, for example, polyvinyl alcohol, polyvinylidine fluorideand its derivatives, hydrocarbons, polyethylene, polystyrene,polyethylene oxide and any polymers including hydrocarbon fragments andheteroatoms. The amount of binder within the cathode may be relativelylow in some cases. For example, the cathode may contain less than about20%, less than about 10%, less than about 5%, less than about 2%, orless than about 1% binder by weight in some embodiments. The use of arelatively low amount of binder may allow for improved fluidcommunication between the electrolyte and the electrode active materials(cathode active material such as sulfur or anode active material such aslithium) and/or between the electrolyte and the electrode conductivematerial. In addition, the use of a low amount of binder may lead toimproved contact between the electrode active material and the electrodeconductive material (e.g., carbon) or improved contact within theelectrode conductive material itself (e.g., carbon-carbon contact).

In some embodiments, an inherently rigid cathode may be produced byinfusing active material (e.g., reticulated Ni foam) into a thin andlight superstructure.

The type of electrolyte and the size of the pores in the cathode may betogether selected such that the resulting capillary forces produced bythe interaction of the electrolyte and the cathode pores resist thedeformation of the cathode. This effect may be particularly useful, forexample, in small electrochemical cells. As another example, thestiffness of the cathode may be enhanced by incorporating reinforcementfibers (e.g., to connect carbon particles) into the cathode.

In some embodiments, the cathode comprises a relatively largeelectrolyte accessible conductive material area. As used herein,“electrolyte accessible conductive material area” is used to refer tothe total surface area of the conductive material (e.g., carbon) thatcan be contacted by electrolyte. For example, electrolyte accessibleconductive material area may comprise conductive material surface areawithin the pores of the cathode, conductive material surface area on theexternal surface of the cathode, etc. In some instances, electrolyteaccessible conductive material area is not obstructed by binder or othermaterials. In addition, in some embodiments, electrolyte accessibleconductive material area does not include portions of the conductivematerial that reside within pores that restrict electrolyte flow due tosurface tension effects. In some cases, the cathode comprises anelectrolyte accessible conductive material area (e.g., an electrolyteaccessible carbon area) of at least about 1 m², at least about 5 m², atleast about 10 m², at least about 20 m², at least about 50 m², or atleast about 100 m² per gram of cathode active material (e.g., sulfur) inthe cathode.

Electrochemical cells described herein may make use of a relatively lowmass of electrolyte relative to the mass of the cathode active material.For example, in some instances, the ratio of electrolyte to cathodeactive material (e.g., sulfur), by mass, within the electrochemical cellis less than about 6:1, less than about 5:1, less than about 4:1, orless than about 3:1.

As mentioned above, some embodiments may include electrochemical devicesin which the application of force is used to enhance the performance ofthe device. Any of the performance metrics outlined herein may beachieved, alone or in combination with each other, while an anisotropicforce is applied to the electrochemical cell (e.g., during charge and/ordischarge of the cell). The magnitude of the anisotropic force may liewithin any of the ranges mentioned below.

In some instances, the cathode structure and/or material and theanisotropic force may be together selected such that the anisotropicforce increases the conductivity within the cathode through charge anddischarge compared to the conductivity in the absence of the anisotropicforce but under otherwise essentially identical conditions.

Additional arrangements, components, and advantages of electrochemicalcells including cathodes that are structurally stable under pressure areprovided in U.S. patent application Ser. No. 12/727,862, filed Mar. 19,2010, entitled, “Cathode for Lithium Battery”, which is incorporatedherein by reference in its entirety.

In some embodiments, an electrochemical cell described herein mayexhibit high active electrode species utilization, i.e., the electrodeactive material may be readily accessible to and may interact with othercomponents or species within the cell during operation, such that cellperformance is enhanced. In some cases, the active material capacity maybe at least 60%, at least 70%, at least 80%, or, in some cases, at least90% of the active material theoretical capacity. The “active materialtheoretical capacity” for a particular material may be calculated usingthe following formula:

Q=1/3600*n*F/M,

wherein:

-   -   Q=theoretical capacity Ah/g (ampere hour per gram),    -   3600=number of seconds in one hour,    -   n=number of electrons involved into electrochemical process per        one molecule of material,    -   F=Faraday constant, 96485 C/mol, and    -   M=material molecular mass, gram.

Those of ordinary skill in the art would be able to calculate the activematerial theoretical capacity and compare it to the experimental activematerial capacity for a particular material to determine whether or notthe experimental capacity is at least 60%, or greater, of thetheoretical capacity.

When elemental sulfur (S) is used as the cathode active material and S²⁻is the desired reaction product, the theoretical capacity (i.e., activematerial theoretical capacity) is 1675 mAh/g. That is, a cell is said toutilize 100% of the total sulfur in the cell when it produces 1675 mAh/gof total sulfur in the cell, 90% of the total sulfur in the cell when itproduces 1507.5 mAh/g of total sulfur in the cell, 60% of the totalsulfur in the cell when it produces 1005 mAh/g of total sulfur in thecell, and 50% of the total sulfur in the cell when it produces 837.5mAh/g of total sulfur in the cell.

In some embodiments, it is possible for the amount of sulfur (or otheractive material) in the region of the cell that is enclosed by thecathode and anode (“available” sulfur) to be less than that of the totalsulfur in the cell. In some cases the electrolyte may be located both inthe region enclosed by the anode and cathode and the region not enclosedby the cathode and anode. For example, during charge/discharge cyclesunder pressure, it is possible for the un-reacted species in the regionenclosed by anode and cathode to move out either by diffusion or by themovement of the electrolyte. The utilization expressed based on this“available” sulfur is the measure of the ability of the cathodestructure to facilitate the conversion of the sulfur in the regionenclosed between the cathode and anode to desirable reaction product(e.g., S²⁻ in the case of sulfur as the cathode active material). Thatis, if all the sulfur available in the region enclosed between thecathode and anode is completely converted to desired reaction product,then the cell will be said to utilize 100% of the available sulfur, andwill produce 1675 mAh/g of available sulfur.

In some embodiments, the cell can be designed in such a way that eitherall of the electrolyte is located in between the region enclosed by theanode and cathode or the transport of un-reacted species from theenclosed region to the outside is completely eliminated. For suchembodiments, the utilization expressed as mAh/g of available sulfur willbe equal to that expressed as mAh/g of total sulfur in the cell.

Sulfur utilization may vary with the discharge current applied to thecell, among other things. In some embodiments, sulfur utilization at lowdischarge rates may be higher than sulfur utilization at high dischargerates. In some embodiments, the cell is capable of utilizing at leastabout 60%, at least about 65%, at least about 70%, at least about 75%,at least about 80%, at least about 85%, at least about 90%, or at leastabout 92% of the total sulfur in the cell over at least one charge anddischarge cycle. In some embodiments, the cell is capable of utilizingat least about 60%, at least about 65%, at least about 70%, at leastabout 75%, at least about 80%, at least about 85%, at least about 90%,or at least about 92% of the available sulfur over at least one chargeand discharge cycle.

The electrochemical cells described herein may be operated usingrelatively high discharge current densities, in some cases. As usedherein, the “discharge current density” refers to the discharge currentbetween the electrodes, divided by the area of the electrode over whichthe discharge occurs, as measured perpendicular to the direction of thecurrent. For the purposes of discharge current density, the area of theelectrode does not include the total exposed surface area of theelectrode, but rather, refers to an imaginary plane drawn along theelectrode surface perpendicular to the direction of the current. In someembodiments, the electrochemical cells may be operated at a dischargecurrent density of at least about 0.1 mA/cm², at least about 0.2 mA/cm²,at least about 0.4 mA/cm² of the cathode surface, or higher. The cellsdescribed herein may also be operated, in some cases, at a highdischarge current per unit mass of active material. For example, thedischarge current may be at least about 100, at least about 200, atleast about 300, at least about 400, or at least about 500 mA per gramof sulfur in the cathode, or higher.

In some cases, the utilization rates of electrochemical cells describedherein may remain relatively high through a relatively large number ofcharge and discharge cycles. As used herein, a “charge and dischargecycle” refers to the process by which a cell is charged from 0% to 100%state of charge (SOC) and discharged from 100% back to 0% SOC. In someembodiments, the electrochemical cell may be capable of utilizing atleast about 60%, at least about 65%, at least about 70%, at least about75%, at least about 80%, at least about 85%, or at least about 90% ofthe sulfur (e.g., total sulfur in the cell, available sulfur) through atleast a first charge and discharge cycle and at least about 1, 2, 10,20, 30, 50, 75, 100, 125, or 135 charge and discharge cycles subsequentto the first charge and discharge cycle. In certain embodiments,electrochemical cells described herein may cycle at least 1 time, atleast 2 times, at least 10 times, at least 20 times, at least 30 times,at least 50 times, at least 75 times, at least 100 times, at least 125times, or at least 135 times subsequent to a first charge and dischargecycle with each cycle having a sulfur utilization (measured as afraction of 1675 mAh/g sulfur (e.g., total sulfur in the cell, availablesulfur) output during the discharge phase of the cycle) of at leastabout 40-50%, at least about 50-60%, at least about 40-60%, at leastabout 40-80%, at least about 60-70%, at least about 70%, at least about70-80%, at least about 80%, at least about 80-90%, or at least about 90%when discharged at a moderately high discharge current of at least about100 mA/g of sulfur (e.g., a discharge current between 100-200 mA/g,between 200-300 mA/g, between 300-400 mA/g, or between 400-500 mA/g).

In some embodiments, the electrochemical cells described herein may havea discharge rate of at least C/30, C/20, C/10, C/5, or C/3.

In some embodiments, electrochemical cells described herein have an areaspecific resistance of less than 50 ohm·cm². That is, the area specificresistance of the entire battery assembly including any electrolyte,separator, or other component(s) of the battery is less than 50 ohm·cm².In certain embodiments, the area specific resistance of anelectrochemical cell (e.g., a lithium battery) is less than 40, 30, 20,10, or 5 ohm·cm². Such area specific resistances can be achieved, insome cases, by using components that reduce the internal resistance orpolarization of the battery, and/or by promoting electronic conductionbetween components (e.g., between an electrode and a current collector).For example, in one embodiment, a lithium battery includes one or moreprimer layers positioned between the active cathode species and thecathode current collector that promotes conducutction between thesecomponents.

Some of the electrochemical cells described herein may maintain capacityover a relatively large number of charge and discharge cycles. Forexample, in some cases, the electrochemical cell capacity decreases byless than about 0.2% per charge and discharge cycle over at least about2, at least about 10, at least about 20, at least about 30, at leastabout 50, at least about 75, at least about 100, at least about 125, orat least about 135 cycles subsequent to a first charge and dischargecycle.

In some embodiments, the electrochemical cells described herein mayachieve relatively high charge efficiencies over a large number ofcycles. As used herein, the “charge efficiency” of the Nth cycle iscalculated as the discharge capacity of the (N+1)th cycle divided by thecharge capacity of the Nth cycle (where N is an integer), and isexpressed as a percentage. In some cases, electrochemical cells mayachieve charge efficiencies of at least about 60%, at least about 70%,at least about 80%, at least about 90%, at least about 95%, at leastabout 97%, at least about 98%, at least about 99%, at least about 99.5%,or at least about 99.9% for the first cycle. In some embodiments, chargeefficiencies of at least about 60%, at least about 70%, at least about80%, at least about 90%, at least about 97%, at least about 98%, atleast about 99%, at least about 99.5%, or at least about 99.9% may beachieved for the 10th, 20th, 30th, 50th, 75th, 100^(th), 125th, or 135thcycles subsequent to a first charge and discharge cycle.

Certain electrochemical cells and electrodes described herein may havehigh energy densities, for example, at least 200 Wh/kg, at least 250Wh/kg, at least 300 Wh/kg, at least 350 Wh/kg, at least 400 Wh/kg, atleast 450 Wh/kg, or at least 500 Wh/kg. Additionally, the cell orelectrode may be designed according to embodiments described herein suchthat it can be cycled at least 100, at least 150, at least 200, at least250, at least 300, at least 350, at least 400, at least 450, or at least500 times during its life.

Some inventive electrochemical cell configurations include anelectrically non-conductive material (e.g., as part of the electrolyte)that is configured to wrap around the edge of an electrode to preventshort circuiting of the electrochemical cell. In some embodiments, theelectrically non-conductive material layer can be arranged such that itincludes first and second portions (one on either side of an electrode)as well as a third portion adjacent the edge of the electrode thatdirectly connects (and, in some cases, is substantially continuous with)the first and second portions. The electrically non-conductive materiallayer can be relatively thin while maintaining relatively highelectrical insulation between the anode and the cathode, allowing one toproduce an electrochemical cell with a relatively low mass and/orvolume. The arrangements described above can be formed, for example, byforming a multi-layer cell structure comprising an electrode and anelectrically non-conductive material layer (e.g., as a coating), andfolding the multi-layer cell structure such that the electricallynon-conductive material covers the convex surface portion of theresulting crease.

The inventors have discovered that, in some embodiments, it can beparticularly advantageous to form the electrically non-conductivematerial layer over an electrode (e.g., via casting, evaporativedeposition, spin-coating, or another process) to form the multi-layercell structure. Producing a multi-layer cell structure via this methodcan be relatively easy, fast, and inexpensive relative to methods inwhich, for example, the electrically non-conductive material layer andelectrode are formed as separate materials and joined together to formthe multi-layer cell structure, which might require complicatedalignment of the electrode and the electrically non-conductive material.In addition, forming the electrically non-conductive material layer overthe electrode can be relatively easy, fast, and inexpensive relative tosystems in which multiple, individual electrodes are place or formed onan electrically non-conductive material, which can also require carefulalignment during both electrode attachment and during folding.

Moreover, forming the electrically non-conductive material layer over anelectrode can also allow for control of the thickness of theelectrically non-conductive material. The formation of relatively thinlayers of electrically non-conductive material can reduce the volumeand/or mass of the multi-layer cell structure, thereby increasing thespecific energy and energy density of the resulting electrochemicalcell.

The inventors have also discovered that short circuiting between theanode and the cathode can be more prevalent when pressure is applied tothe electrochemical cell, as a reduction in the distance between theanode and the cathode can increase the possibility of a short circuitwithin the cell. In one aspect, the use of particular arrangements ofelectrically non-conductive materials can allow for the application of aforce to an electrochemical cell without producing short circuitsbetween the anode and the cathode. In addition, the configurations ofelectrically non-conductive materials described herein can reduce theprobability of a short circuit within the cell after repeated chargingand discharging cycles (e.g., due to dissolution and re-plating ofelectrode materials).

FIGS. 8A-8D include exemplary cross-sectional schematic diagramsillustrating a method of arranging an electrically non-conductivematerial layer, according to one set of embodiments. In FIG. 8A,multi-layer cell structure 800 comprises substrate 810 and electrode 812positioned adjacent each other. In some embodiments, electrode 812 canbe formed over substrate 810. For example, electrode 812 might bedeposited (e.g., via vacuum deposition of a metal, mixture of metals, orother suitable material), onto substrate 810. As another example,electrode 812 might be formed on substrate 810 by a casting process(e.g., by depositing and drying a slurry comprising electrode activematerial on a substrate). In other embodiments, electrode 812 andsubstrate 810 might be formed as separate entities and adhered orotherwise joined together to form the structure illustrated in FIG. 8A.In still other embodiments, substrate 810 and electrode 812 might beprovided as a pre-assembled multi-layer cell structure.

In some embodiments, such as the set of embodiments illustrated in FIG.8A, electrode 812 does not completely cover substrate 810, but rather,edge portions 811 of substrate 810 are left exposed. Such arrangementscan be useful in forming electrical contacts, for example, when thesubstrate supports or is used as a current collector in the assembledelectrochemical cell. It should be understood, however, that in otherembodiments, electrode 812 can be arranged to substantially completelycover substrate 810.

In FIG. 8B, multi-layer cell structure 800 further compriseselectrically non-conductive material layer 814 positioned adjacentelectrode 812, such that electrode 812 is between electricallynon-conductive material layer 814 and substrate 810. As described inmore detail below, the electrically non-conductive material layer 814can form all or part of the electrolyte of the electrochemical cellformed from multi-layer cell structure 800, in some cases. In someembodiments, electrically non-conductive material layer 814 is adheredto electrode 812. In some instances, at least a portion of electricallynon-conductive material layer 814 is covalently bonded to electrode 812.

In some embodiments, electrically non-conductive material layer 814 canbe formed over electrode 812. For example, electrically non-conductivematerial layer 814 might be applied over electrode 812 and formed inplace, for example using a casting process (e.g., by depositing anddrying a slurry comprising electrode active material on a substrate).Exemplary methods for performing such a deposition are described, forexample, in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley et al., each of which is incorporatedby reference in its entirety for all purposes. In some embodiments, theelectrically non-conductive material layer can be deposited by methodssuch as electron beam evaporation, vacuum thermal evaporation, laserablation, chemical vapor deposition, thermal evaporation, plasmaassisted chemical vacuum deposition, laser enhanced chemical vapordeposition, jet vapor deposition, and extrusion. The electricallynon-conductive material layer may also be deposited by spin-coatingtechniques. A method for depositing, for example, crosslinked polymerlayers includes flash evaporation methods, for example, as described inU.S. Pat. No. 4,954,371 to Yializis. A method for depositing, forexample, crosslinked polymer layers comprising lithium salts may includeflash evaporation methods, for example, as described in U.S. Pat. No.5,681,615 to Affinito et al. The technique used for depositing theelectrically non-conductive material layer may depend on the type ofmaterial being deposited, the thickness of the layer, etc. Depositingthe electrically non-conductive material layer on an electrode can beadvantageous, in some embodiments, because they can allow for thedeposition of relatively thin layers of electrically non-conductivematerial, which can reduce the size and weight of the finalelectrochemical cell.

In other embodiments, electrically non-conductive material layer 814,substrate 810, and electrode 812 can be formed as separate entities andadhered or otherwise joined to the rest of the multi-layer cellstructure. In still other embodiments, substrate 810, electrode 812, andelectrically non-conductive material layer 814 might be provided as apre-assembled multi-layer cell structure.

The substrate 810, electrode 812 and/or the electrically non-conductivematerial layer 814 (or other layers of the multi-layer cell structure)can be a substantially continuous layer, in some embodiments.“Substantially continuous,” as used to describe a relationship betweentwo sections or layers of a structure, means that any region of thestructure between the sections or layers is essentially identical to thesections or layers. E.g., a substantially continuous sheet of material,folded upon itself or folded around a different material, can define twoor more sections that remain part of the substantially continuous sheet.

In some embodiments, the substrate 810, electrode 812, electricallynon-conductive material layer 814, and/or other material layersdescribed herein can be substantially free of macroscopicdiscontinuities. A layer that is “substantially free of macroscopicdiscontinuities” is one that includes no region with a maximumcross-sectional dimension measured substantially parallel to the layerthat is greater than the thickness of the layer, made up of a material(or mixture of materials) that is different than the composition of therest of the layer. As specific examples, a layer with substantially novoids can be substantially free of macroscopic discontinuities. Inaddition, a porous material layer can be substantially free ofmacroscopic discontinuities if the maximum cross-sectional dimension ofthe pores within the layer is less than the thickness of the layer. Aporous material with pore sizes greater than the thickness of the layerof porous material, however, would not be substantially free ofmacroscopic discontinuities. In addition, a material that includes abulk material and an island of a second material with a maximumcross-sectional dimension greater than the thickness of the materialwithin the bulk material would not be substantially free of macroscopicdiscontinuities.

As shown in FIG. 8B, electrically non-conductive material layer 814includes a first substantially planar surface 820 facing away fromelectrode 812 and substrate 810 and a second substantially planarsurface (at interface 822) facing electrode 812 and substrate 810. Inaddition, electrode 812 includes a first substantially planar surface(at interface 822) facing electrically non-conductive material layer 814and facing away from substrate 810 as well as a second substantiallyplanar surface (at interface 824) facing substrate 810 and facing awayfrom electrically non-conductive material layer 814. Substrate 810includes a first substantially planar surface (at interface 824) facingelectrode 812 and electrically non-conductive material layer 814 and asecond substantially planar surface 826 facing away from electrode 812and electrically non-conductive material layer 814.

Within the context of the multi-layer cell structure configurationsdescribed, for example, in FIGS. 8A-8D, a surface (or surface portion)is said to be “facing” an object when the surface and the object aresubstantially parallel, and a line extending normal to and away from thebulk of the material comprising the surface intersects the object. Forexample, a first surface (or first surface portion) and a second surface(or second surface portion) can be facing each other if a line normal tothe first surface and extending away from the bulk of the materialcomprising the first surface intersects the second surface. A surfaceand a layer can be facing each other if a line normal to the surface andextending away from the bulk of the material comprising the surfaceintersects the layer. A surface can be facing another object when it isin contact with the other object, or when one or more intermediatematerials are positioned between the surface and the other object. Forexample, two surfaces that are facing each other can be in contact orcan include one or more intermediate materials between them.

Within the context of the multi-layer cell structure configurationsdescribed, for example, in FIGS. 8A-8D, a surface (or surface portion)is said to be “facing away from” an object when the surface and theobject are substantially parallel, and no line extending normal to andaway from the bulk of the material comprising the surface intersects theobject. For example, a first surface (or first surface portion) and asecond surface (or second surface portion) can be facing away from eachother if no line normal to the first surface and extending away from thebulk of the material comprising the first surface intersects the secondsurface. A surface and a layer can be facing away from each other if aline normal to the surface and extending away from the bulk of thematerial comprising the surface intersects the layer. In someembodiments, a surface and another object (e.g., another surface, alayer, etc.) can be substantially parallel if the maximum angle definedby the surface and the object is less than about 10°, less than about5°, less than about 2°, or less than about 1°.

The multi-layer cell structure can be folded along an axis to form afolded structure. In some embodiments, the multi-layer cell structurecan be folded such that first and second portions of a surface of theelectrode (e.g., first and second portions of a surface that faces awayfrom the electrically non-conductive material layer) face each other.For example, in the set of embodiments illustrated in FIGS. 8B-8C,multi-layer cell structure 800 in FIG. 8B is folded along axis 830(which extends into and out of the page) in the direction of arrows 832to form the multi-layer cell structure illustrated in FIG. 8C. Surfaceportions 824A and 824B of electrode 812, originally both facing awayfrom electrically non-conductive material layer 814 in FIG. 8B, havebeen reoriented in the structure of FIG. 8C such that they are facingeach other. As shown in FIG. 8C, surface portions 824A and 824B includean intermediate material (substrate 810) between them. However, in otherembodiments, surface portions 824A and 824B can be in contact.

By folding the multi-layer cell structure in this way, a portion 836 ofthe electrically non-conductive material layer is arranged such that itis oriented over the convex surface portion of the folded edge ofelectrode 812. In some cases, the electrically non-conductive materiallayer can substantially cover the edge of electrode 812. Having aportion (such as portion 836) of the electrically non-conductivematerial over the folded edge of electrode 812 can be useful inpreventing short circuiting between electrode 812 and subsequentelectrodes positioned over electrically non-conductive material layer814.

Additional electrodes can also be included in the multi-layer cellstructure. In the set of embodiments illustrated in FIG. 8D, electrodes840 and 842 are positioned adjacent electrically non-conductive materiallayer 814. When arranged in this fashion, the electricallynon-conductive material layer includes a first portion 846 betweenelectrodes 812 and 840 and a second portion 848 between electrodes 812and 842. In addition, first and second portions 846 and 848,respectively, are directly connected by portion 836. Within the contextof the multi-layer cell structure configurations described, for example,in FIGS. 8A-8D, two components or portions of a component are said to be“directly connected” or in “direct contact” when a line can be drawnconnecting the two portions or components without passing through aregion with a substantially different composition. In the set ofembodiments illustrated in FIG. 8D, first and second portions 846 and848 are also substantially continuous, although they need not be in allembodiments.

One or both of electrodes 840 and 842 can be formed over electricallynon-conductive material layer 814. For example, electrode 840 and/or 842might be deposited (e.g., via vacuum deposition) or cast (e.g., as adried slurry), onto material layer 814. In other embodiments, electrode840 and/or 842 can be formed as separate entities and adhered orotherwise joined to the multi-layer cell structure. While two additionalelectrodes 840 and 842 are illustrated in FIG. 8D, it should beunderstood that, in other embodiments, only one additional electrode(e.g., only electrode 840) can be included in the multi-layer cellstructure.

In some embodiments, electrode 840 and/or electrode 842 are adhered toelectrically non-conductive material layer 814. In some instances, atleast a portion of electrode 840 and/or electrode 842 is covalentlybonded to electrically non-conductive material layer 814.

The polarities of the electrodes can be selected to produce anelectrochemical cell. In some embodiments, electrode 812 can be of afirst polarity while electrode 840 (and 842, if present) can be of asecond, opposite polarity. Generally, two electrodes are of oppositepolarities if one is an anode and the other is a cathode. For example,electrode 812 can be an anode while electrode 840 (and 842, if present)can be a cathode. In other cases, electrode 812 can be a cathode whileelectrode 840 (and 842, if present) can be an anode.

Electrical contact can be made with the electrodes using any suitabletechnique. In the set of embodiments illustrated in FIG. 8D, electricalcontact can be made with electrode 812 by using an electricallyconductive substrate 810. Substrate 810 can include an electricallyconductive bulk material or an electrically non-conductive bulk materialcoated with an electrically conductive material. Electrical contact canbe made with electrodes 840 and/or 842 by incorporating currentcollectors 844A and 844B, respectively, into the multi-layer cellstructure.

In the embodiments illustrated in FIGS. 8A-8D, and in other embodimentsdescribed herein, one or more additional layers may be positionedbetween the layers shown in the figures. For example, one or moreadditional layers may be positioned between substrate 810 and electrode812 such as, for example, a release layer, which can be used to removethe substrate prior to folding multi-layer cell structure 800. Inaddition, one or more additional layers may be positioned between therelease layer and the substrate. Furthermore, one or more layers may bepositioned between other components of the multi-layer cell structure.For example, one or more primer layers can be positioned between acurrent collector and an electrode layer to facilitate adhesion betweenthe layers. Examples of suitable primer layers are described inInternational Patent Application Serial No. PCT/US2008/012042, publishedas International Publication No. WO 2009/054987, filed Oct. 23, 2008,and entitled “Primer For Battery Electrode”, which is incorporatedherein by reference in its entirety. In addition, one or more layers canbe placed between an electrode and the electrically non-conductivematerial layer. For example, one or more layers can be positionedbetween electrode 812 and electrically non-conductive material layer814, between electrode 840 and electrically non-conductive materiallayer 814, and/or between electrode 842 and electrically non-conductivematerial layer 814. Of course, in other embodiments, substrate 810 andelectrode 812 can be in contact, electrode 812 and electricallynon-conductive material layer 814 can be in contact, electricallynon-conductive material layer 814 and electrode 840 can in contact,and/or electrically non-conductive material layer 814 and electrode 842can be in contact. In addition, in some cases electrode 840 and/or 842can be in contact with a current collector 844A and 844B, respectively,while in other cases, one or more materials can be positioned betweenelectrode 840 and its current collector and/or electrode 842 and itscurrent collector.

Some embodiments of the invention relate to the relative positions ofthe components (or portions thereof) described herein. In someembodiments, the multi-layer cell structure (or an electrochemical cellcontaining the multi-layer cell structure) can include the followinglayers positioned in the order described (e.g., traced along arrow 860in FIG. 8D), optionally with any number of other layers of the same ordifferent material intervening the described layers: a first electrodelayer portion having a first polarity (e.g., a portion of electrode 840in FIG. 8D), a second electrode layer portion having a second polarity(e.g., a portion of electrode 812 above substrate 810 in FIG. 8D), athird electrode layer portion having the second polarity (e.g., aportion of electrode 812 below substrate 810 in FIG. 8D), and a fourthelectrode layer portion having the first polarity (e.g., a portion ofelectrode 842 in FIG. 8D). In some cases, as in the embodimentsillustrated in FIG. 8D, the second and third electrode layer portionsare portions of a single, substantially continuous electrode. Inaddition, in some cases, no electrode portion having the first polarityis positioned intervening the second and third electrode layer portions.In FIG. 8D, for example, only substrate 810 (which is not an electrode)is positioned between the second electrode layer portion (e.g., aportion of electrode 812 above substrate 810 in FIG. 8D) and the thirdelectrode layer portion (e.g., a portion of electrode 812 belowsubstrate 810 in FIG. 8D).

In some embodiments, a multi-layer cell structure (or an electrochemicalcell containing the multi-layer cell structure can include a substratewith a first substrate surface portion (e.g., a substrate surfaceportion adjacent surface portion 824A of electrode 812) and a secondsubstrate surface portion facing away from the first substrate surfaceportion (e.g., a substrate surface portion adjacent surface portion 824Bof electrode 812). The multi-layer cell structure can also comprise afirst electrode with a first portion adjacent the first substratesurface portion (e.g., the portion of electrode 812 above the substratein FIG. 8D) and a second portion adjacent the second substrate surfaceportion (e.g., the portion of electrode 812 below the substrate in FIG.8D). In addition, the multi-layer cell structure can include a secondelectrode (e.g., electrode 840 in FIG. 8D, although electrode 842 couldalso be included, in addition to of in place of electrode 840) with afirst surface portion facing the first portion of the first electrode(e.g., the surface of electrode 840 at interface 850A) and a secondsurface portion facing away from the first surface portion of the secondelectrode (e.g., the surfaces of electrode 840 facing top currentcollector 844A). In addition, the multi-layer cell structure can includea substantially continuous, electrically non-conductive material layer(e.g., layer 814 in FIG. 8D) having a first portion between the firstportion of the first electrode and the first surface portion of thesecond electrode (e.g., portion 846 of electrically non-conductivematerial layer 814), a second portion adjacent the second surfaceportion of the first electrode (e.g., portion 848 of electricallynon-conductive material layer 814), and a third portion in directcontact with the first and second portions (e.g., portion 836 ofelectrically non-conductive material layer 814).

The electrically non-conductive material layer can have any suitablethickness. In some embodiments, a relatively thin electricallynon-conductive material layer can be employed, which can reduce thevolume and/or weight of the multi-layer cell structure, therebyincreasing the specific energy and energy density of an electrochemicalcell fabricated using the multi-layer cell structure. In someembodiments, the electrically non-conductive material layer can have anaverage thickness of less than about 100 microns, less than about 50microns, less than about 20 microns; less than about 10 microns; lessthan about 5 microns; less than about 1 micron; at least about 0.1microns and less than about 100, 50, 20, 10, 5, or 1 micron; at leastabout 0.5 microns and less than about 100, 50, 20, 10, 5, or 1 micron;or at least about 1 micron and less than about 100, 50, 20, 10, or 5microns. In some cases, the average distance between the outermostsurface of electrode 812 (e.g., at interface 822 in FIGS. 8C and 8D) andthe innermost surface of electrode 840 and/or electrode 842 (e.g., atinterfaces 850A and 850B, respectively, in FIG. 8D) can be less thanabout 100 microns, less than about 50 microns, less than about 20microns; less than about 10 microns; less than about 5 microns; lessthan about 1 micron; at least about 0.1 microns and less than about 100,50, 20, 10, 5, or 1 micron; at least about 0.5 microns and less thanabout 100, 50, 20, 10, 5, or 1 micron; or at least about 1 micron andless than about 100, 50, 20, 10, or 5 microns.

In some embodiments, the electrodes and the electrically non-conductivematerial layer can be constructed and arranged such that, when a voltageis applied to the electrodes and across the dry electricallynon-conductive material layer (i.e., prior to the addition of any fluidsuch as a liquid electrolyte), a relatively high electrical resistanceis maintained. In some cases, the electrical resistance between an anodeand a cathode within the dry multi-layer cell structure is at leastabout 100 Ohms, at least about 1000 Ohms, at least about 10 kiloOhms, atleast about 100 kiloOhms, at least about 1 megaOhm, or at least about 10megaOhms when a voltage of at least about 1 volts is applied across theanode and the cathode. One of ordinary skill in the art would be capableof making such a measurement by applying a voltage drop across thematerial between the anode and the cathode within the multi-layer cellstructure and measuring the resulting resistance using a multimeter.

In some cases, the electrical resistance through the thickness of thedry electrically non-conductive material layer (i.e., prior to theaddition of any fluid such as a liquid electrolyte) is at least about100 Ohms, at least about 1000 Ohms, at least about 10 kiloOhms, at leastabout 100 kiloOhms, at least about 1 megaOhm, or at least about 10megaOhms when a voltage of at least about 1 volts is applied across theanode and the cathode. One of ordinary skill in the art would be capableof making such a measurement by applying a voltage drop through thethickness of the non-electrically conductive material layer (e.g., byattaching electrodes to surfaces of the non-electrically conductivematerial layer that are facing away from each other) and measuring theresulting resistance using a multimeter.

The electrically non-conductive material layer can comprise any materialcapable of separating or insulating the anode and the cathode from eachother to prevent short circuiting, while being constructed and arrangedto permit the transport of ions between the anode and the cathode. Insome embodiments, all or part of the electrically non-conductivematerial layer can be formed of a material with a bulk resistivity of atleast about 10⁴, at least about 10⁵, at least about 10¹⁰, at least about10¹⁵, or at least about 10²⁰ Ohm meters.

In some embodiments, the electrically non-conductive material layer canbe the electrolyte of the electrochemical cell formed from themulti-layer cell structure. In other cases, the electricallynon-conductive material layer can be a layer separate from theelectrolyte of the electrochemical cell formed from the multi-layer cellstructure (i.e., the electrochemical cell can include an electrolytelayer separate from the electrically non-conductive material layer).

All or part of the electrically non-conductive material layer can beformed of a solid electrolyte, in some embodiments. In addition toelectrically insulating the anode from the cathode, the solidelectrolyte can be ionically conductive, thereby allowing for thetransfer of ions between the anode and the cathode. Examples of usefulsolid polymer electrolytes include, but are not limited to thosedescribed elsewhere herein.

In some embodiments, all or part of the electrically non-conductivematerial layer can be formed of a gel. As used herein, the term “gel”refers to a three-dimensional network comprising a liquid and a bindercomponent, in which the liquid is entrained by and not allowed to flowthrough the binder. Gels can be formed when liquids are entrained withina three-dimensional network of solids upon applying the liquid to thesolid network. In some cases, the three-dimensional network within a gelcan comprise a liquid entrained within a polymer (e.g., a cross-linkedpolymer). One of ordinary skill in the art would be capable ofdetermining the difference between a gel and other combinations of asolid and a fluid (e.g., a porous separator and a liquid solvent) bymeasuring, for example, the absorption stiffness of the gel via adibutyl phthalate (DBP) uptake test. Generally, upon exposure of thebinder component of a gel to a liquid, the weight of the gel willincrease, while the weight of a porous separator will not substantiallyincrease. In some embodiments, the binder component of the gel is ableto take up liquid in the substantial absence of pores greater than about10 microns or greater than about 1 micron. The binder component of a gelcan be substantially free of pores in some cases. Examples of useful gelpolymers for use in electrically non-conductive material layers includethe gel polymers described elsewhere herein, among others.

In some embodiments, at least part of the electrically non-conductivematerial can be formed of a solid, electrically non-conductive materialthat is partially or substantially filled with a liquid electrolyte. Insome such embodiments, the solid material that is partially orsubstantially filled with a liquid electrolyte can serve as theelectrolyte for the electrochemical cell. The solid, electricallynon-conductive material can, in some embodiments, be substantiallyionically non-conductive. In other cases, the solid, electricallynon-conductive might be ionically conductive, and the liquid electrolytecan be used to produce a combined structure with an enhanced ionicconductivity (relative to that of the solid portion of the combination).A variety of solid, electrically non-conductive separator materials areknown in the art. and are described elsewhere herein.

As in other embodiments described elsewhere herein, substrate 810 can beremoved prior to finishing the assembly of the electrochemical cell, insome embodiments. In the set of embodiments illustrated in FIGS. 8A-8D,substrate 810 can be removed prior to or after folding the multi-layercell stack. Of course, in other embodiments, such as those illustratedin FIG. 8D, substrate 810 can be incorporated within the final assembledstructure.

In the compounds and compositions of the invention, the term “alkyl”refers to the radical of saturated aliphatic groups, includingstraight-chain alkyl groups, branched-chain alkyl groups, cycloalkyl(alicyclic) groups, alkyl substituted cycloalkyl groups, and cycloalkylsubstituted alkyl groups. The alkyl groups may be optionally substitutedwith additional groups, as described further below. In some embodiments,a straight chain or branched chain alkyl may have 30 or fewer carbonatoms in its backbone, and, in some cases, 20 or fewer. In someembodiments, a straight chain or branched chain alkyl has 12 or fewercarbon atoms in its backbone (e.g., C₁-C₁₂ for straight chain, C₃-C₁₂for branched chain), 6 or fewer, or, 4 or fewer. In some embodiments,cycloalkyls may have from 3-10 carbon atoms in their ring structure, or5, 6 or 7 carbons in the ring structure. Examples of alkyl groupsinclude, but are not limited to, methyl, ethyl, propyl, isopropyl,cyclopropyl, butyl, isobutyl, tert-butyl, cyclobutyl, hexyl,cyclochexyl, and the like.

The term “heteroalkyl” refers to an alkyl group as described herein inwhich one or more carbon atoms is replaced by a heteroatom. Suitableheteroatoms include oxygen, sulfur, nitrogen, phosphorus, and the like.Examples of heteroalkyl groups include, but are not limited to, alkoxy,amino, thioester, and the like.

The terms “alkene” and “alkyne” refer to unsaturated aliphatic groupsanalogous in length and possible substitution to the alkyls describedabove, but that contain at least one double or triple bond respectively.

The terms “heteroalkenyl” and “heteroalkynyl” refer to unsaturatedaliphatic groups analogous in length and possible substitution to theheteroalkyls described above, but that contain at least one double ortriple bond respectively.

As used herein, the term “halogen” or “halide” designates —F, —Cl, —Bror —I.

The term “methyl” refers to the monovalent radical —CH₃, and the term“methoxy” refers to the monovalent radical —OCH₃.

The term “aromatic” is given its ordinary meaning in the art and refersto cyclic groups comprising a conjugated pi electron system.

The term “aryl” refers to aromatic carbocyclic groups, optionallysubstituted, having a single ring (e.g., phenyl), multiple rings (e.g.,biphenyl), or multiple fused rings in which at least one is aromatic(e.g., 1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl).That is, at least one ring may have a conjugated pi electron system,while other, adjoining rings can be cycloalkyls, cycloalkenyls,cycloalkynyls, aryls and/or heterocyclyls. The aryl group may beoptionally substituted, as described herein. “Carbocyclic aryl groups”refer to aryl groups wherein the ring atoms on the aromatic ring arecarbon atoms. Carbocyclic aryl groups include monocyclic carbocyclicaryl groups and polycyclic or fused compounds (e.g., two or moreadjacent ring atoms are common to two adjoining rings) such as naphthylgroups.

The terms “heteroaryl” refers to aryl groups comprising at least oneheteroatom as a ring atom.

The term “heterocycle” refers to cyclic groups containing at least oneheteroatom as a ring atom, in some cases, 1 to 3 heteroatoms as ringatoms, with the remainder of the ring atoms being carbon atoms. Suitableheteroatoms include oxygen, sulfur, nitrogen, phosphorus, and the like.In some cases, the heterocycle may be 3- to 10-membered ring structures,or 3- to 7-membered rings, whose ring structures include one to fourheteroatoms. The term “heterocycle” may include heteroaryl groups,saturated heterocycles (e.g., cycloheteroalkyl) groups, or combinationsthereof. The heterocycle may be a saturated molecule, or may compriseone or more double bonds. In some case, the heterocycle is a nitrogenheterocycle, wherein at least one ring comprises at least one nitrogenring atom. The heterocycles may be fused to other rings to form apolycylic heterocycle. The heterocycle may also be fused to aspirocyclic group. In some cases, the heterocycle may be attached to amolecule (e.g., a polymer) via a nitrogen or a carbon atom in the ring.

Heterocycles include, for example, thiophene, benzothiophene,thianthrene, furan, tetrahydrofuran, pyran, isobenzofuran, chromene,xanthene, phenoxathiin, pyrrole, dihydropyrrole, pyrrolidine, imidazole,pyrazole, pyrazine, isothiazole, isoxazole, pyridine, pyrazine,pyrimidine, pyridazine, indolizine, isoindole, indole, indazole, purine,quinolizine, isoquinoline, quinoline, phthalazine, naphthyridine,quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline,triazole, tetrazole, oxazole, isoxazole, thiazole, isothiazole,phenanthridine, acridine, pyrimidine, phenanthroline, phenazine,phenarsazine, phenothiazine, furazan, phenoxazine, pyrrolidine, oxolane,thiolane, oxazole, oxazine, piperidine, homopiperidine(hexamethyleneimine), piperazine (e.g., N-methyl piperazine),morpholine, lactones, lactams such as azetidinones and pyrrolidinones,sultams, sultones, other saturated and/or unsaturated derivativesthereof, and the like. The heterocyclic ring can be optionallysubstituted at one or more positions with such substituents as describedherein.

The term “alkoxy” refers to the group, O-alkyl.

The term “alkoxyalkyl” refers to an alkyl group substituted with analkoxy group. For example, “—CH₂CH₂—OCH₃” is an alkoxyalkyl group.

The terms “amine” and “amino” are art-recognized and refer to bothunsubstituted and substituted amines, e.g., a moiety that can berepresented by the general formula: N(R′)(R″)(R′″) wherein R′, R″, andR′″ each independently represent a group permitted by the rules ofvalence.

The terms “ortho” (or “o-”), “meta” (or “m-”) and “para” (or “p-”) applyto 1,2-, 1,3- and 1,4-disubstituted benzenes, respectively. For example,the names 1,2-dimethylbenzene, ortho-dimethylbenzene, ando-dimethylbenzene are synonymous.

As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds, “permissible” being inthe context of the chemical rules of valence known to those of ordinaryskill in the art. It will be understood that “substituted” also includesthat the substitution results in a stable compound, e.g., which does notspontaneously undergo transformation such as by rearrangement,cyclization, elimination, etc. In some cases, “substituted” maygenerally refer to replacement of a hydrogen with a substituent asdescribed herein. However, “substituted,” as used herein, does notencompass replacement and/or alteration of a key functional group bywhich a molecule is identified, e.g., such that the “substituted”functional group becomes, through substitution, a different functionalgroup. For example, a “substituted phenyl” group must still comprise thephenyl moiety and can not be modified by substitution, in thisdefinition, to become, e.g., a pyridine ring. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, aromatic and nonaromaticsubstituents of organic compounds. Illustrative substituents include,for example, those described herein. The permissible substituents can beone or more and the same or different for appropriate organic compounds.For purposes of this invention, the heteroatoms such as nitrogen mayhave hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valencies of theheteroatoms.

Examples of substituents include, but are not limited to, halogen,azide, alkyl, aralkyl, alkenyl, alkynyl, cycloalkyl, hydroxyl, alkoxyl,amino, nitro, sulfhydryl, imino, amido, phosphonate, phosphinate,carbonyl, carboxyl, silyl, ether, alkylthio, sulfonyl, sulfonamido,ketone, aldehyde, ester, heterocyclyl, aromatic or heteroaromaticmoieties, —CF₃, —CN, aryl, aryloxy, perhaloalkoxy, aralkoxy, heteroaryl,heteroaryloxy, heteroarylalkyl, heteroaralkoxy, azido, amino, halide,alkylthio, oxo, acylalkyl, carboxy esters, -carboxamido, acyloxy,aminoalkyl, alkylaminoaryl, alkylaryl, alkylaminoalkyl, alkoxyaryl,arylamino, aralkylamino, alkylsulfonyl, -carboxamidoalkylaryl,-carboxamidoaryl, hydroxyalkyl, haloalkyl, alkylaminoalkylcarboxy-,aminocarboxamidoalkyl-, cyano, alkoxyalkyl, perhaloalkyl,arylalkyloxyalkyl, and the like.

The following documents are incorporated herein by reference in theirentireties for all purposes: U.S. Pat. No. 7,247,408, filed May 23,2001, entitled “Lithium Anodes for Electrochemical Cells”; U.S. Pat. No.5,648,187, filed Mar. 19, 1996, entitled “Stabilized Anode forLithium-Polymer Batteries”; U.S. Pat. No. 5,961,672, filed Jul. 7, 1997,entitled “Stabilized Anode for Lithium-Polymer Batteries”; U.S. Pat. No.5,919,587, filed May 21, 1997, entitled “Novel Composite Cathodes,Electrochemical Cells Comprising Novel Composite Cathodes, and Processesfor Fabricating Same”; U.S. patent application Ser. No. 11/400,781,filed Apr. 6, 2006, published as U. S. Pub. No. 2007-0221265, andentitled “Rechargeable Lithium/Water, Lithium/Air Batteries”;International Patent Apl. Serial No.: PCT/US2008/009158, filed Jul. 29,2008, published as International Pub. No. WO/2009017726, and entitled“Swelling Inhibition in Lithium Batteries”; U.S. patent application Ser.No. 12/312,764, filed May 26, 2009, published as U.S. Pub. No.2010-0129699, and entitled “Separation of Electrolytes”; InternationalPatent Apl. Serial No.: PCT/US2008/012042, filed Oct. 23, 2008,published as International Pub. No. WO/2009054987, and entitled “Primerfor Battery Electrode”; U.S. patent application Ser. No. 12/069,335,filed Feb. 8, 2008, published as U.S. Pub. No. 2009-0200986, andentitled “Protective Circuit for Energy-Storage Device”; U.S. patentapplication Ser. No. 11/400,025, filed Apr. 6, 2006, published as U.S.Pub. No. 2007-0224502, and entitled “Electrode Protection in bothAqueous and Non-Aqueous Electrochemical Cells, including RechargeableLithium Batteries”; U.S. patent application Ser. No. 11/821,576, filedJun. 22, 2007, published as U.S. Pub. No. 2008/0318128, and entitled“Lithium Alloy/Sulfur Batteries”; patent application Ser. No.11/111,262, filed Apr. 20, 2005, published as U.S. Pub. No.2006-0238203, and entitled “Lithium Sulfur Rechargeable Battery FuelGauge Systems and Methods”; U.S. patent application Ser. No. 11/728,197,filed Mar. 23, 2007, published as U. S. Pub. No. 2008-0187663, andentitled “Co-Flash Evaporation of Polymerizable Monomers andNon-Polymerizable Carrier Solvent/Salt Mixtures/Solutions”;International Patent Apl. Serial No.: PCT/US2008/010894, filed Sep. 19,2008, published as International Pub. No. WO/2009042071, and entitled“Electrolyte Additives for Lithium Batteries and Related Methods”;International Patent Apl. Serial No.: PCT/US2009/000090, filed Jan. 8,2009, published as International Pub. No. WO/2009/089018, and entitled“Porous Electrodes and Associated Methods”; U.S. patent application Ser.No. 12/535,328, filed Aug. 4, 2009, published as U.S. Pub. No.2010/0035128, and entitled “Application of Force In ElectrochemicalCells”; U.S. patent application Ser. No. 12/727,862, filed Mar. 19,2010, entitled “Cathode for Lithium Battery”; U.S. patent applicationSer. No. 12,471,095, filed May 22, 2009, entitled “Hermetic SampleHolder and Method for Performing Microanalysis Under ControlledAtmosphere Environment”; a U.S. patent application Ser. No. 12/862,581,filed on Aug. 24, 2010, entitled “Release System for Electrochemicalcells (which claims priority to Provisional Patent Apl. Ser. No.61/236,322, filed Aug. 24, 2009, entitled “Release System forElectrochemical Cells”); U.S. Provisional Patent Application Ser. No.61/376,554, filed on Aug. 24, 2010, entitled “ElectricallyNon-Conductive Materials for Electrochemical Cells;” and U.S. patentapplication Ser. Nos. 12/862,563; 12/862,551; 12/862,576; and Ser. No.12/862,581, each of which was filed on Aug. 24, 2010, each entitled“Electrochemical Cells Comprising Porous Structures Comprising Sulfur”(and each of which claim priority to U.S. Provisional Application No.61/237,903, filed Aug. 28, 2009, entitled “Electrochemical CellsComprising Porous Structures Comprising Sulfur” to Scordilis-Kelley etal). All other patents and patent applications disclosed herein are alsoincorporated by reference in their entirety for all purposes.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. A final electrochemical cell, comprising: a firstelectrode comprising: a base electrode material layer comprising a firstactive electrode species, wherein the first active electrode speciescomprises lithium; and a release layer, wherein the release layer has agreater adhesive affinity to a surface of the first electrode relativeto its adhesive affinity to a carrier substrate on which the firstelectrode was formed; a second electrode comprising a second activeelectrode species; and an electrolyte, wherein an anisotropic force isapplied to the final electrochemical cell during at least one period oftime during charge and/or discharge of the final electrochemical cell,wherein the anisotropic force comprises a component normal to a surfaceof the first electrode, and wherein the component defines a pressure ofat least about 4.9 N/cm² and causes a surface morphology of at least oneof the first electrode or the second electrode to be affected.
 2. Thefinal electrochemical cell of claim 1, further comprising at least oneceramic layer adjacent the base electrode material layer.
 3. The finalelectrochemical cell of claim 1, wherein the first electrode is an anodeand the second electrode is a cathode.
 4. The final electrochemical cellof claim 1, wherein the first active electrode species comprises lithiummetal.
 5. The final electrochemical cell of claim 1, wherein the baseelectrode material layer comprises lithium metal and a Li—Z alloy, whereZ is a metal or semiconductor and is present in an amount greater than100 ppm but less than or equal to 10 wt % of the alloy.
 6. The finalelectrochemical cell of claim 5, wherein the first electrode is ananode, and wherein Z is substantially uniformly dispersed throughout abulk portion of the anode prior to 10^(th) discharge of the finalelectrochemical cell.
 7. The final electrochemical cell of claim 1,further comprising a current collector positioned between the releaselayer and the base electrode material layer.
 8. The finalelectrochemical cell of claim 2, wherein the ceramic layer comprisespores, and wherein at least a portion of the pores are filled with apolymer.
 9. The final electrochemical cell of claim 1, wherein theelectrolyte comprises an external additive having the formula LiR or(Li—X)_(n)R′, wherein R comprises a heteroalkyl or heteroaryl group,optionally substituted; R′ comprises an alkyl or aryl group, optionallysubstituted; X is a heteroatom; and n is an integer equal to or greaterthan
 1. 10. The final electrochemical cell of claim 1, wherein theelectrolyte comprises a lithium compound additive that can be producedthrough reaction between the lithium of the first electrode and at leastone other species of the final electrochemical cell during charge and/ordischarge of the final electrochemical cell, and wherein the reaction issubstantially irreversible under normal charge and/or discharge of thefinal electrochemical cell.
 11. The final electrochemical cell of claim1, wherein the first electrode and the electrolyte together have amaximum thickness of 500 microns or less.
 12. The final electrochemicalcell of claim 1, wherein the electrolyte comprises one or more N—Oadditives, the one or more N—O additives comprising one or more ofinorganic nitrates, organic nitrates, organic nitrites, and organicnitro compounds.
 13. The final electrochemical cell of claim 1, whereinthe electrolyte comprises a solvent comprising one or more of an acyclicether, a cyclic ether, a polyether, and a sulfone.
 14. The finalelectrochemical cell of claim 1, wherein the electrolyte comprises oneor more lithium salts, the one or more lithium salts comprising one ormore of LiNO₃, LiSCN, LiCF₃SO₃, and LiN(CF₃SO₂)₂.
 15. The finalelectrochemical cell of claim 1, wherein the second electrode comprisesa conductive carbon-containing material.
 16. The final electrochemicalcell of claim 1, wherein the second electrode comprises a porousstructure comprising a plurality of pores having a total pore volumedefined by the total of each of the individual pores volumes, and atleast about 50% of the total pore volume is occupied by particles havinga maximum diameter of between about 0.1 microns and about 10 microns.17. The final electrochemical cell of claim 16, wherein the porousstructure comprises at least one of carbon, a metal, a polymer, and aceramic.
 18. The final electrochemical cell of claim 16, wherein thepressure defined by the component of the anisotropic force is at leastabout 78 Newtons/cm², and wherein the second electrode comprises aporous structure having a porosity of at least about 30% during theapplication of the anisotropic force.
 19. The final electrochemical cellof claim 1, wherein the second electrode comprises a porous structurehaving a yield strength of at least 200 N/cm².
 20. The finalelectrochemical cell of claim 1, wherein the pressure defined by thecomponent of the anisotropic force is at least about 4.9 N/cm² and lessthan about 250 N/cm².
 21. The final electrochemical cell of claim 1,wherein the first electrode is an anode comprising an anode activesurface, wherein the anisotropic force affects surface morphology of theanode active surface to inhibit an increase in anode active surface areathrough charge and discharge, and wherein, in the absence of theanisotropic force but under otherwise essentially identical conditions,the anode active surface area is increased to a greater extent throughcharge and discharge cycles.